In this order of Mammalia
of the body is still more fish-like than in the Sirenia.
is no trace of a neck, the contour of the head passing gradually
into that of the body. A horizontally-flattened caudal
fin is always present; and, very generally, the dorsal integument
is produced into a median, laterally-compressed dorsal
fin. The body is incased in a thick smooth integument, beneath
which a very thick layer of fat is deposited. Hairs are
almost entirely absent in the adult state.
As in the recent Sirenia,
the anterior limbs alone are
present. Externally they do not present any indication of
division into brachium, antibrachium, and manus, but have the
form of a broad, flattened paddle, without any vestiges of nails.
The one or two apertures by which the cavity of the nose
opens externally, are always situated at the top of the head,
and far removed from the extremity of the snout. There is
no third eyelid, and the very small auditory apertures are totally
devoid of any pinna. The teats are two, and, in the
female, are lodged in depressions on each side of the vulva.
The articular surfaces of the centra of the vertebrae are
flat, and the epiphyses usually remain distinct for a long time.
The spinal column, as a whole, is remarkable for the shortness
of its cervical, and the length of its lumbar region, there
being sometimes a greater number of lumbar than of dorsal
vertebrae. There is no sacrum. The caudal vertebrae are only
distinguishable from the posterior lumbo-sacral vertebrae by
their chevron-bones. The second vertebra of the neck is devoid
of any odontoid process; and it very commonly happens
that more or fewer of the cervical vertebrae, the bodies of
which are often so short as to be mere disks, are anchylosed
together, either by their arches, or by their centra, or by both.
The centra of all the succeeding vertebrae are large in proportion
to their arches, and the inter-vertebral fibro-cartilages are
exceedingly thick, so as to confer great flexibility and elasticity
on the spine. The arches of the hinder dorsal vertebrae,
and of those of the lumbar and caudal regions, are not articulated
together by zygapophyses. The centra of the posterior
caudal vertebras lose their processes and become polygonal.
Very few of the ribs become connected with the sternum
at their distal ends; and, in contradistinction to what happens
in most Mammalia
, the proximal ends of the majority of the
ribs are connected only with the transverse processes of the
vertebrae, and not with their bodies.
The skull is even more remarkably modified than the vertebral
column. The brain-case itself has a spheroidal form;
while the jaws are greatly prolonged, the principal enlargement
of the upper jaw taking place in the region which lies in
front of the nasal aperture. The basis cranii
, as a whole, is
ramarkably broad, and its upper surface concave from before
backward, the sella turcica
being very slightly indicated.
The parietal bones are comparatively small, and do not meet
in a sagittal suture, as they do in other Mammalia;
supraoccipital, with an interparietal bone, being interposed between
them, and extending forward so as to unite with the
frontals. Each frontal bone is produced outward into a great
bony plate which covers the orbit. The squamosal bone sends
a very large and stout zygomatic process forward to meet this
supra-orbital prolongation of the frontal. The proper jugal
bone, on the other hand, which bounds the orbit below, is exceedingly
slender. The very large maxilla extends backward
and outward in contact with the frontal, or even overlapping
the greater part of its surface; and it stretches forward to
very near the anterior end of the snout, so that almost the
whole of the gape is bounded by the maxilla.
The premaxillae, on the other hand, though very long, inasmuch
as they occupy the whole length of the jaw in the middle
line, from the anterior nasal aperture to the end of the
snout, are almost entirely excluded from the gape.
The nasal bones are always short; and, sometimes, are
mere bony tuberosities united with the frontal bones behind
the anterior nasal aperture. The turbinal bones are almost
always rudimentary, and the nasal passages are nearly vertical,
in consequence, for the most part, of the rudimentary condition
and shortness of the nasal bones.
The periotic bones are loosely connected with the squamosal
and tympanic, and are usually united with the other
bones of the skull only by cartilage, so that they fall out very
readily in the dry skull. The tympanic bones are commonly
of very considerable size, thick and scroll-shaped.
The lower jaw has hardly any coronoid process, and its
ramus has no perpendicular portion, the condyle being situated
upon its posterior extremity. The body of the hyoid is a very
broad plate of bone, and has two pair of stout, well-ossified
are devoid of clavicles. If the spine of the
scapula is present, it is a low ridge situated close to the anterior
edge of the bone; but it commonly terminates in a long
acromion process, and, sometimes, there is a conspicuous,
straight, and flattened coracoid. The humerus is short, and
the articular surfaces at its distal end are, in all recent Cetacea
flat facets inclined to one another at an angle. The ulna and
the radius are short, laterally-compressed bones, without any
movement upon one another; and, in all recent Cetacea
are not freely movable upon the humerus. The carpus is often
imperfectly ossified. When the carpal bones are complete,
they are polygonal and imbedded in a fibrous tissue; not
united by articulations provided with synovial membranes.
The digits do not exceed five in number, but there are always
more than three phalanges in some of them.
The pelvis is represented by two bones which lie parallel
with the axis of the vertebral column, give attachment to the
corpora cavernosa in the male, and, therefore probably represent the ischia.
They are elongated, convex upward and concave
downward, and are connected with the vertebral column
only by fibrous tissue. In some few Cetacea (Balaenoidea)
ossicles, which lie on the outer side of the pelvic bone, appear
to represent the femur, but no further indication of a hindlimb
has been discovered.
In most of the Cetacea
, the muscles which, in other Mammalia
move the antibrachium and the manus, are absent,
those which move the humerus upon the shoulder-blade being,
In no recent Cetacean have the teeth any vertical successors,
nor more than a single root. The alveoli are often
incompletely separated from one another. The number of the
teeth varies very greatly, but they are almost alwavs nearly
uniform in character. There appear to be no salivary glands.
The stomach is complicated, being divided into, at fewest,
three chambers, of which the first is a kind of paunch lined by
a thick epithelium, while the second and the third are more
elongated, the last stomach being that in which digestion
The arteries and veins form great plexuses, or relia mirabila
and these are especially conspicuous in the cavity of
the thorax, upon each side of the vertebral column, and in the
The soft palate is remarkably long and muscular. The
epiglottis and the arytenoid cartilages are more or less produced,
so as to give the glottis the shape of a funnel, the apex
of which is embraced by the soft palate, in such a manner as
to form a continuous air-passage from the posterior nares to
the larynx, on each side of which the food passes. The very
short trachea, before it divides into the bronchi, gives off the
so-called "third bronchus" to the right lung, as in the Bears,
Walruses, and Ruminants.
|Fig. 104. - Lateral and superior views of the skull of a foetal Whale (Balaena Australia)-The jugal bones are absent, and the figure does not sufficiently indicate the outward
curvature of the ramus of the mandible (Mn.).
The kidneys are deeply subdivided into lobules. In the
male the testes always remain in the abdomen, and there are
no vesiculae seminales. The penis is devoid of a bone. The
uterus of the female is deeply divided into two horns, and the
villi of the foetus are scattered over its chorion, as in other
mammals with a diffuse placentation.
The Cetacea are divisible into three groups: the Balaenoidea
, and the Phocodontia
(For further information respecting the
characters of the recent Cetacea
refer the reader to Prof. Flowers's very valuable memoir "On the Osteology
," published in the "Transactions of the Zoological
Society for 1867.")
In the Balaenoidea
the nasal chambers communicate
with the exterior by two apertures, which are capable of being
shut at the will of the animal, and are called spiracles. These
are not connected with any saccular dilatations of the nasal
passages, situated between the skull and the integument.
In the spinal column, no rib has a complete neck and capitulum,
the heads of even the most anterior ribs being united with the bodies of the vertebrae
only by ligament. The chief connection of all the ribs, therefore, and the only connection
of most of them, is with the transverse processes of the vertebrae.
The short and broad sternum unites only with the first
rib, and the union is direct, so that there are no sternocostal
The skull (Fig. 104) is exceedingly large in proportion to
the body, and nearly symmetrical. The nasal bones, Nu.
though short, are longer, and more like those of ordinary
mammals, than is the case in other Cetacea.
The maxilla, Mx.,
extends outward in front of the great supraorbital process
of the frontal, Fr.,
but it does not cover the frontal bone.
There is a distinct lachrymal. Each ramus of the mandible, Mn.
, is convex outward and concave inward; and the space
between the rami of the mandible is very much greater than
the width of the maxillo-premaxillary part of the skull, which
tapers to its anterior end, and is more or less convex upward
and concave inferiorly. The two rami of the mandible are
connected only by ligament at the symphysis.
|Fig. 105. - "Ear-bones" of the adult Balaena Australia. - Seen from within in the upper
figure; from without in the lowor. Eu., Eustachian canal; Au.,external auditory
meatus; Sty., ossified root of the styloid process.
Minute teeth are developed in foetal Baloenidae
, but are
very soon lost, and their place taken by the so-called Whalebone
plates. Each of these is triangular, with a
thick, smooth outer edge, somewhat concave from above downward,
which, in the natural position of the plates, is nearly
vertical, and is covered by the great lower lip. The upper
edge of the plate, also slightly concave, is attached to a transverse
elevation of the gum covering the palate. Vascular
papillae extend from this ridge into cavities of corresponding
dimensions, which lie, parallel with one another, in the baleen
plate. The third side of the triangular baleen plate, somewhat
convex and sloping from the middle line above, downward and
outward, gives origin to a number of filamentous processes,
into which the baleen appears to be, as it were, frayed out.
When the mouth is shut, these frayed edges of the numerous
and close-set baleen plates, which are longest in the middle
of each series, and shortest at each end, enclose a cavity, the
bottom of which is occupied by the large and fleshy tongue.
By raising the tongue, whatever solid matters are enclosed in
the mouth can be forced back into the pharynx and swallowed;
while the water in which they were suspended is driven out
between the baleen plates. The Whale feeds by putting this
gigantic strainer into operation, as it swims through the shoals
of minute molluscs, crustaceans, and fishes, which are constantly
found at the surface of the sea. Opening its capacious
mouth, and allowing the sea-water, with its multitudinous
tenants, to fill the oral cavity, the Whale shuts the lower jaw
upon the baleen plates, and, straining out the water through
them, swallows the prey stranded upon its vast tongue.
In some of the Balaenoidea
, e.g., Balaena rostrata
cricoid cartilage and the rings of the trachea are incomplete
in front, and a large air-sac is developed in the cricothyroid
space. The Balaenoidea
possess olfactory nerves and a distinct,
though small, olfactory apparatus. The sclerotic coat
of the eyeball is enormously thick, and the optic nerve is surrounded
by a rete-mirdbile.
The tympanic membrane is connected
with the malleus by ligament. The semicircular canals
are very small, but the cochlea is large, and makes only 1 1/2
turns. The muscles of the antibrachium and manus are not
|Fig. 106. - Upper (A), under (B), and lateral (C) views of the skull of a foetal Cachalot
(Physeter).-The nasal bones arc not presented in the upper view, and the hinder ead
of the jugal is displaced from its natural connection with the squamosal in (C),
The right Whale (Balaena
), and the Fin-fishes (Megaptera, Balaenoptera,
belong to this division.
In the Delphinoidea
the nasal chambers open by only
a single spiracle on the top of the head; and saccular dilatations
of various dimensions are developed from the walls of the
passage which connects this aperture with the bony nasopalatine
passages, and lie between the integument and the
outer surface of the skull.
More or fewer of the anterior ribs have heads and necks,
the capitula articulating with the bodies of the vertebrae, as
in other Mammalia
. The elongated sternum is, almost always,
composed of several pieces arranged in a longitudinal
series; and cartilaginous, or ossified, sternal ribs are present
in greater or smaller number. The nasal bones, which are
very short, and have their upper surfaces tubercle-like, are
more or less asymmetrically developed, as are also the maxillae;
so that the facial part of the skull appears distorted.
The maxillae are expanded behind, and cover the orbital process
of the frontal bone wholly or partially. The lachrymal
bone is usually small and confluent with the slender jugal, but
it may be large and distinct. The rami of the mandible are
not arcuated outward, and they become united in a longer or
shorter symphysis. The mandible, as a whole, is not sensibly
broader than the corresponding portion of the maxillo-premaxillary
part of the skull.
Teeth always exist after birth, and are never replaced by
baleen plates. They are usually numerous, but sometimes few
and deciduous. Occasionally, only one or two teeth persist,
and these, as in the Narwhal, may take the form of immensely-
To this division belong the Physeteridae Platanistidae
possess functional teeth only in the lower
jaw. The asymmetry of the skull is strongly pronounced;
and, in the adult, the maxillary and frontal bones are produced,
so as to form a sort of basin upon the upper and anterior
surface of the skull. The pterygoids meet in the middle
line below, and the mandibular symphysis is sometimes extremely
The greater number of the cervical vertebrae are anchylosed.
The hinder ribs lose their tubercular, but retain their
capitular articulation with the vertebrae. The costal cartilages
are not ossified. The pectoral limbs are small, and a
dorsal fin is usually present.
The proper Sperm Whales (Physeterinae
) have an enormous
head, with a quadrate truncated snout, at the anterior
superior angle of which the spiracle is placed. The teeth
become fully developed only in the lower jaw. The cranial
basin is immense, and is filled by a loose connective tissue, in
which the peculiar fat known as spermaceti
is contained. Ambergris
is a sort of bezoar, found in the alimentary canal of tho
Cachalot, and seemingly derived from the fatty matter contained in the Cephalopoda
on which the Cetacean feeds. In
the other group of the Physeteridae
to which the Bottlenosed Whale (Hyperoodon)
there are only one or two pairs of fully-formed teeth in
the mandible. Some recent and many fossil (middle and later
tertiary) genera of the Cetaceans are remarkable for the elongated
rostrum formed by the solid ossification and anchylosis
of the ethmoid, premaxillae, and maxillae.
are fluviatile or estuarine Cetacea
which occur in the Ganges and in the rivers of South America.
The cervical vertebrae are not anchylosed, and the costal cartilages
are not ossified. The tubercula and capitula of the
ribs blend together posteriorly. The symphysis of the mandibles
is extremely long and the jaws are narrow. Numerous
teeth with compressed fangs are found in both jaws. The
eyes are small, and in Platanista
they are rudimentary.
In the Dephinidae
lastly (Dolphins, Porpoises, Grampuses),
the teeth are usually numerous in both jaws, though
the Narwhal is an exception to this rule, as has already been
The anterior cervical vertebrae are generally anchylosed
together. The posterior ribs lose their capitula and become
articulated only with the transverse processes of the vertebrae.
The costal cartilages are well ossified. The symphysis of the
mandible does not exceed one third of the rami in length, and
the frontal and maxillary bones are not especially produced
upward at their edges.
As the common Porpoise (Phoccaena communis)
, which is
a member of this group, is the Cetacean which is most likely
to come within reach of the student, it may be useful to
speak at some length of its more interesting anatomical peculiarities.
The adult animal is usually about five feet long, and is
covered with a smooth integument upon which no hair is to
be discovered, though a few hairs are visible about the mouth
in the young animal. The contour of the anterior part of the
head is very convex, and presents, in the middle line, the
spiracle or blow-hole, which has the form of a crescent with
the points turned downward and forward. The eyes are small
end placed low down, close to the posterior end of the gape
of the mouth, which is bounded by dense and rigid lips. The
aperture of the ear lies about an inch and three-quarters behind
the eye, and is so minute as to be discovered with difficulty.
The genital aperture is placed a long way in front of
the anus in the male; while, in the female, the interval, in
which the fossse which lodge the teats are situated, is much
less. There is a conspieuous vertical dorsal fin in addition to
the flattened caudal fin. Immediately beneath the skin is a
thick layer of blubber, as in other Cetacea.
In the spongy texture of all the bones, the absence of medullary
cavities in those of the limbs, and in the long persistent
separability of the epiphyses of the centra of the vertebrae,
the Porpoise resembles other Cetacea;
as it does in the
shortness of the cervical, and the length of the lumbar, region
of the spinal column.
The seven cervical vertebrae are all anchylosed together, and
the atlas, which is very large in proportion to the rest, overlaps
them above and at the sides. The centra of the hinder
cervicals are so short and broad that they are mere plates of
bone. There are twenty-eight dorso-lumbar vertebrae, of which
fifteen are dorsal. In all but the most anterior of these
vertebrae, the zygapophyses are abortive; and long accessory
processes, developed from the front-part of the neural arches,
loosely embrace the spine of the vertebrae in front. This arrangement,
together with the thickness of the intervertebral
ligaments, gives great flexibility to the spinal column. The
transverse processes of the hinder dorsal, and of the lumbar,
vertebra are very long. There are five pairs of true ribs. The
sternebrae anchylose into an elongated sternum. The anterior
caudal vertebrae are provided with large chevron-bones, and
their transverse processes exhibit notches through which
branches of the aorta pass.
In consequence of the globular form of the brain-case, and
the prolongation of the jaws, the skull has a flask-like shape.
There is a slight want of symmetry about the base of the upper
jaw, but it is hardly appreciable.
In a longitudinal section, the flatness and the upwardly
concave contour of the base of the skull; the extreme shallowness
of the sella turcica;
the presence of an ossified tentorium;
and the broad imperforate anterior wall, in the place of the
cribriform plate of the ethmoid, are striking features. The
synchondrosis between the basi-and presphenoid is persistent.
On the base of the skull the basi-occipital gives off great processes
outward and downward, to form, together with a paramastoid
prolongation of the exocoipital, and the squamosal, a
chamber in which the anchylosed tympanie and periotic bones
are contained. The ex-and supra-occipitals, together with the
interparietals, form the whole back wall and middle of the
roof of the cranium, separating the parietals completely, and
the frontals largely, and reaching the nasal bones.
The basi-sphenoid is anchylosed with the small and almost
horizontal alisphenoids, and there are no sphenoidal pterygoid
processes. The parietals are small, and occupy only the under
and lateral portions of the brain-case. The frontal bones are
very broad and expanded, and are completely anchylosed together,
where they form the front wall of the brain-case. Posteriorly
and above, they diverge to receive the interparietal.
The supra-orbital processes are extremely large, and are
directed forward and outward, not backward and outward, as
in the Whalebone Whales. The greater part of the superior
surface of the frontals and of their orbital processes is rough
and covered over by the expanded maxillary bones, which
allow only a narrow, transverse, smooth, band-like surface,
formed by the frontals, to be seen on the upper and anterior
region of the skull. The rough surface is marked by two
shallow grooves which pass from below upward, and are convex
toward one another and to the middle line. Corresponding
grooves exist on the under side of the expanded proximal
ends of the maxillaries; and, when these are in their natural
positions, the coadapted grooves form two canals, which are
blind in front and above. These, in the natural state, are full
of air, and communicate with the air-chambers at the base of
the skull and with the Eustachian tubes.
The narrow premaxillae are anchylosed with the inner
margins of the maxillae, and contribute only a very small portion
of the alveolar margin of the upper jaw. The alveoli are
not completely separated from one another. The pterygoid
bones do not unite in the palate. They have a peculiar excavated
form, and are notched for the passage of the ends of
the Eustachian tubes into the nasal passages. These are nearly
vertical and are separated by the large and strong vomer.
Their superior apertures are left quite uncovered in consequence
of the small size, tubercular form, and backward position
of the nasal bones. The squamosal is relatively small, but
has the characteristically cetacean, large, zygomatic process;
this extends forward nearly to the posterior end of the supraorbital
process, and gives attachment to the slender jugal.
The periotic bones form a dense osseous mass, which is
anchylosed with the no less heavy and thick, scroll-shaped
tympanic. The pars mastoidea
of the periotic mass fits pretty
accurately into a recess of the chamber which has already been
described; and is thus held in position in the dry skull, though
it is very easily detached.
When the tympano-periotic
bone and all the facial bones
are removed, only two pair of foramina are visible in the base
of the skull. The anterior pair give exit to the second, third,
fourth, the anterior division of the fifth and the sixth nerves,
and these answer to the optic and sphenorbital foramina. The
posterior pair take the place of the oval, posterior lacerated,
and jugular foramina, and the precondyloid foramina open into
them posteriorly. The rami of the mandibles are only united
by a short symphysis. The body of the hyoid is broad and
hexagonal, and has two slender, anterior, and two broad and
flat, posterior, cornua.
In the natural position the fore-limbs stand out from the
body with their flat surfaces looking upward and downward;
the upper surface being directed a little backward, and the
lower a little forward. The tuberosity of the short humerus
is directed forward. The carpus contains six or seven ossifications.
The number of phalanges in the digits is two, eight,
six, three, two, counting the pollex as the first.
The pelvic bones are elongated, slightly curved, osseous
styles. They lie with their long axes parallel to the vertebral
column, their convex sides upward, and their smaller ends forward,
within an inch of the centra of the vertebrae, their
hinder-ends being close to the third chevron-bone of the tail.
The front-ends are about an inch apart. Behind its centre,
each bone presents a flattened thickening for the attachment
of the corpus cavemosum of its side.
The cutaneous muscle is very largely developed, and lies
between two layers of blubber, the thick surperficial one separating
it from the skin, and the thin deep layer from the subjacent
muscles. It may be said to be disposed in two broad
layers, a dorsal and a ventral, on each side; these extend from
the occipital crest, and from the rami of the mandibles, to the
tail. Both these divisions send off strong bundles to the humerus,
which act as powerful adductors, abductors, protractors,
and retractors of the fin. There is no trapezius
, and the representative
of the latissimus dorsi
is very small. A strong occipito-humeralis
, from the paramastoid to the tuberosity of
the humerus, seems to represent the cleido-mastoid and clavicular
deltoid. A costo-humeralis
extends from the sternum to the
inner tuberosity of the humerus. A small coraco-branchialis
from the apex of the coracoid to the inner tuberosity of the
humerus. The pectoralis major
seems to be represented by a
muscle which arises from the sternum, close to the attachment of
the third and fourth ribs, and is inserted into the ulna. The triceps
is represented by tendinous fibres in which muscle
cannot always be detected, which extend from the posterior face
of the humerus to the ulna. The other muscles of the forearm
and all those of the manus are absent. The dorsal muscles
form a thick continuous mass from the end of the tail to the
occiput; and, on the ventral side of the spinal column, the
subcaudal muscles are similarly continued forward, as far as
the middle of the thorax. An ischio-caudalis
passes, on each
side, from the anterior chevron-bones to the ischium. Between
their attachments is an aponeurosis which supports the anus;
ischio-cavernous muscles pass from the ischia to the corpora
The diaphragm has no tendinous centre. Its pillars are
very thin, and, extending between the kidneys and the spine,
become tendinous, and are attached to the ventral faces of the
vertebrae, as far as the ninth lumbar. A strong fibrous aponeurosis
is continued back over the subvertebral muscles to the
pelvic bones. Between these bones and the ends of the transverse
processes of the twenty-eighth and twenty-ninth vertebrte
(counting from the first dorsal) the aponeurosis is so stout
as to form an almost distinct fibrous band, which occupies the
place of an ilium. The ureter lies between the ischio-vertebral
fascia and the peritonaeum.
The teeth are small and numerous, and their crowns are
obtuse and constricted. The passage of the pharynx is divided
in the middle, the soft palate being prolonged into a muscular
funnel, the opening of which closely fits the constricted
neck of the long cone into which the epiglottis and the arytenoid
cartilages are produced. Thus the arrangement which is
transitory in the Marsupial is permanent in the Cetacean.
The stomach is divided into three sacs. The first is large,
conical, and lined by a coarse white epithelial coat. The gullet
opens directly into it. The second stomach communicates
with the first by an aperture which is close to the cardiac end
of the gullet, and is surrounded by a very prominent rugose
lip. A curved passage about one inch long and capable of
admitting the finger, lined by a white epithelium similar to
that of the first, leads into the second stomach. The second
stomach is lined by an extremely vascular and soft mucous
membrane, with about ten strong longitudinal folds, separated
by deep sulci, interrupted by transverse ridges. A narrow
and curved canal leads from this into the third stomach, which
has a tubular form and is bent upon itself. Its lining membrane
is quite smooth. A small, circular, pyloric aperture
places this in communication with the dilated commencement
of the duodenum, which has sometimes been regarded as a
fourth stomach. Its lining membrane presents longitudinal
ragae continuous with those of the duodenum itself. The conjoined
pancreatic and biliary ducts open just beyond the dilated
part of the duodenum. There is no coecum, or demarcation
between the large and small intestines. The bilobed
liver has no gall-bladder.
In the heart the fossa ovalis is distinct, but there is neither
Eustachian nor Thebesian valve. The vena cava inferior is
long and wide, but is not especially dilated near the heart.
Muscular fibres are not continued on to it from the diaphragm.
The aorta and pulmonary arteries are not dilated at their origins.
The arteries have a great tendency to break up into
plexuses. Thus the internal carotids form great networks
which communicate with vertebral plexuses, extending throughout
the entire spinal canal. The brachial artery divides into
two branches, and these subdivide into innumerable parallel
twigs. The intercostal arteries are the chief source of the
large thoracic plexuses, which lie at the sides of the vertebral
column in the dorsal half of the thorax. Finally, an arterial rete mirabile
surrounds the caudal aorta. The veins form
plexuses corresponding to, and mixed up with, those of the
arteries; and a very large venous plexus lies on the subvertebral
muscles in the abdomen and thorax.
The respiratory apparatus of the Porpoise presents many
remarkable peculiarities. The contour of the front part of the
head, as bounded by the integument, is very convex—the corresponding
facial region of the skull, on the contrary, is very
concave. The interval between the two is occupied, in part,
by fibrous and fatty tissue; and, in part, by a singularly sacculated spiracular chamber
, which connects the single spiracle
with the double external nares of the skull. Two valves, an
anterior and a posterior, lie immediately above these external
nares and close the communication between them and the
chamber, except at such times as it is forced open from below.
Each nasal passage remains distinct from the other as far as
the valves, the middle of each of the latter being fastened to
the septum, so that there may be said to be a pair of valves
for each opening between the passages and the spiracular
rharaber. Each nasal passage, after it ceases to be surrounded
by bone, sends off two diverticida, one forward and one backward.
The anterior, which lies between the anterior valve
and the premaxilia, is a simple sac, lined with a thin, black,
smooth membrane. The posterior diverticulum lies between
the posterior valve and the ethmoid and nasal bones. It is
incompletely divided by a sort of shelf, is prolonged forward,
round, and in front of, the anterior valve, and ends blindly in
the middle line above the anterior sac. The spiracular chamber
itself is produced, on each side, into a large lateral sac, the
walls of which are raised in strong parallel ridges, and covered
with a black papillose integument. The walls of these sacs
are strong and elastic. Layers of muscular fibres pass from
the occipital ridge to the posterior lip of the spiracle, and
from the edges of the maxillae to its anterior lip. Their action
is necessarily to open the spiracle and compress the sacs.
There is no sphincter, the form of the spiracle causing it to be
naturally shut by the fitting together of its walls, and the
pressure of the water upon them.
When a Porpoise comes to the surface to "blow," the
shape of the posterior, concave lip of the crescentic spiracle
does not sensibly alter; but the anterior, convex lip is pulled
downward and forward, its surface becoming somewhat depressed,
and its free edge nearly straight-so that the aperture,
when fully dilated, assumes the form of a half-moon. At the
same time, the air is expelled with a rushing sound. The
inspiratory act must be very rapid, as the spiracle remains
open for only a very short time after expiration ends. When
the larger Cetacea
come up to breathe, the expired vapor
suddenly condenses into a cloud; and, if expiration commencea
before the spiracle is actually at the surface, a certain quantity
of spray may be driven up along with the violent current of
the expelled air. This gives rise to the appearance termed
the "spouting" of Whales, which does not arise, as it is
commonly said to do, from the straining off of the sea-water
swallowed with the food, and its expulsion by the nostrils.
The epiglottis, in front, and the arytenoid cartilages behind,
are prolonged into a tapering tube, dilated at its summit
into a knob. The muscular soft palate embraces the neck of
this knob so closely that it cannot be withdrawn without
considerable effort. And thus, during life, the nasal airpassages
and the glottis are kept perfectly continuous; while
the Porpoise dashes through the water, open-mouthed, after
its prey. The point at which the extra bronchus to the right
lung is given off is separated by four rings from the bifurcation
of the trachea. The lungs are not lobed and their tissue is
very dense and elastic.
The cerebral hemispheres are, taken together, broader than
they are long. In the upper view they leave not more than a
seventh of the length of the cerebellum exposed, while they
overlap it largely at the sides. The outer surface of the hemispheres
is extremely convoluted, the gyri being numerous and
separated by deep sulci. There is a well-marked Sylvian
fissure, with a central lobe, or insula. A rudiment of a posterior
cornu has been observed, in the lateral ventricle. The
corpus callosum is small, relatively to the size of the hemispheres,
and the anterior commissure is almost obsolete. The
medulla oblongata has corpora trapezoidea
. The olfactory
nerves are wanting-a circumstance which agrees with the
entire absence of ethmoidal turbinals. The eye has a thick
sclerotic, and there is a choanoid muscle; no nictitating membrane
The external auditory aperture is so small as to be easily
overlooked. The meatus auditorius is a narrow undulating
tube about two inches long. The tympanic membrane is concave
externally; and, as is usual in the Cetacea
, is connected
by a ligament with the handle of the malleus. There is only
a small aperture in the stapes. The tensor tympani
in Carnivores, from a fossa in the periotic ossification.
The Eustachian tube passes through the notch in the pterygoid
and opens into the nasal passage on the inner side of that
notch. Close to its commencement it communicates, by an
oval aperture, with a remarkable air-chamber, which extends
backward between the periotic mass and the basis cranii
forward to the under side of the expanded part of the maxilla,
where it opens into the canal between the maxilla and the
frontal already described. These chambers, like the bronchi,
are generally full of nematoid worms. The testes and penis
of the male are enormous in proportion to the size of the
The penis is devoid of a bone, and, ordinarily, is bent up
in the long preputial sheath.
are represented only by Zeuglodon,
, and other large extinct cetaceans of the tertiary
epoch. These remarkable fossil forms constitute connecting
links between the Cetacea
and the aquatic Carnivora
cervical vertebrae are distinct and unanchylosed, nearly resembling
those of the Rhyncoceti.
The caudal vertebrae have
their transverse processes perforated vertically, as in many Cetacea.
The distal ends of the ribs are enlarged somewhat
as in the Sirenia.
The skull is symmetrical, and the nasal
bones, though still short, are longer than those of any other
cetacean. The zygomatic processes of the squamosal are large
and thick, and the supraorbital processes of the frontals wide
and expanded as in the Cetacea.
The scapula appears to have had a spine and acromion like
that of Manatus.
The humerus is compressed from the side,
and has true articular surfaces upon its distal end, although
they are of small size.
The molar teeth have laterally-compressed crowns with
serrated edges and two fangs, resembling those of many seals,
diifers from all the other Cetacea
in the circumstance
that some of its teeth have vertical successors.