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  Section: Anatomy of Vertebrate Animals » The Classification and Organization of the Mammalia
 
 
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The Cynomorpha

 
     
 

a. The Cynomorpha are distinguished from the other group by being essentially quadrupedal, and usually provided with a tail, which is never prehensile. The femur and tibia, taken together, are longer than the humerus and the radius. The outer inferior incisors are not larger than the inner ones, but are often smaller. The crowns of the molar teeth present two transverse ridges, a third being present, in some genera on the last inferior molar.

All the Cynomorpha have ischial callosities, which sometimes attain a very large size, and are brightly colored.

The dorso-lumbar region of the spinal column is concave toward the ventral aspect, and the lumbo-sacral angle is very large. The atlas has narrow transverse processes. The ordinary number of dorso-lumbar vertebrae is nineteen, of which twelve, or thirteen, are dorsal; and seven, or six, lumbar. The middle cervical vertebrse have short spines, which are not bifurcated at their extremities. In the posterior dorsal and anterior lumbar vertebrae, the mammillary and accessory processes may be enlarged and interlock. The long transverse processes of the lumbar vertebrse bend forward. The sacrum usually contains only three anchylosed vertebrae. The caudal vertebrae vary in number, from three in Inuus (where they form little more than a coccyx), to as many as thirty-one. In the anterior part of the tail the vertebrae are provided with subvertebral, or chevron, bones.

The thorax is laterally compressed, and the manubrium of the sternum is broad; but the six or seven sternebrae which follow it are compressed and constricted.

The skull presents a considerable range of variation. In the Semnopitheci and Colobi, the frontal region is rounded, the facial angle is comparatively large, and the ascending portion of the ramus of the mandible is high. In the Macaci and Cynocephali, on the other hand, the supra-orbital ridges become so much enlarged as to hide the forehead; and the horizontal portion of the ramus of the mandible is much larger than the ascending portion, in accordance with the great production of the upper jaw, and the consequent low facial angle. In many of the Cynocephali, longitudinal osseous ridges are developed upon the maxillae, and greatly increase the brutishness of their aspect. Sagittal and lambdoidal crests may appear along the lines of the corresponding sutures. There is no distinct mastoid process; and the styloid process is not ossified.
The parietal bones do not unite with the alisphenoids, being separated from them by the union of the squamosals with the frontals. The brain-case is flattened and elongated, and the convex roofs of the orbits project into it, and greatly diminish the capacity of its frontal portion. The olfactory fossae are very deep, and sometimes almost tubular. The two frontal bones send thick processes across the base of the skull, which unite over the junction of the presphenoid and the ethmoid, and thus narrow the entrance to the olfactory fossae. The basicranial axis is shorter than the cerebral cavity, but is still proportionally long. The occipital foramen lies in the posterior sixth of the base of the skull, and it looks obliquely backward and downward. The premaxillo-maxillary suture never disappears until long after the second dentition as complete, and may persist throughout life. The palate is long and narrow. The nasal bones are fiat, and early anchylose into one bone.

The scapula is relatively longer and narrower than that of Man; but the spine lies at right angles to the vertebral border, and the supra-spinous is much smaller than the infraspinous fossa.

The axis of the articular head of the humerus is not directed upward and inward, but upward and backward; the bicipital groove lies on the inner side; and the shaft of the bone is so bent that it is convex forward. In all these characters the fore-limb shows its relation to the function of support. The radius exhibits modiiications which have the same signification. Its proximal head is transversely elongated, and lies somewhat in advance of the ulna, articulating more largely with the humerus than in the higher Apes. The neck of the radius (between the head and the bicipital tuberositv) fits more closely to the ulna, and hence the movements of pronation and supination are restricted.

There are nine bones in the carpus. The pisiforme is much elongated, making a sort of heel for the manus. Together with the cuneiforme, it furnishes an articular face for the ulna. The distal articular surface of the trapezium is saddle-shaped, and the pollex is usually complete, though short relatively to the other digits. In Colobus it is rudimentary.

The pelvis is long and narrow. The ilia are narrow bones with much-excavated posterior and outer faces. Their crests generally lie opposite the transverse processes of the penultimate lumbar vertebra. The long axis of the ilium and that of the anterior ramus of the pubis cut one another nearly at a right angle; while the long axis of the ilium and that of the posterior ramus of the ischium lie nearly in one straight line. The symphysis pubis is very long, and the subpubic arch correspondingly reduced. The posterior ends of the ischia are everted, broad, and rough, for the attachment of the callous pads of integument. The femur has a round ligament. The tarsus has not more than one-third the length of the foot. The calcaneal process is flattened from side to side, and has a pulley-like excavation upon its posterior extremity. The tibial facet of the astragalus is inclined slightly inward, as well as upward, and its outer edge is raised. The distal division of the tarsus, consisting of the cuboid and navicular, with the cuneiform bones, is capable of a considerable amount of rotatory motion upon the astragalus and the calcaneum. The ento-cuneiform bone is large, and has a transversely-convex articular surface for the metatarsal of the hallux. Consequently the latter (which is short, reaching to only about the middle of the proximal phalanx of the second digit) is capable of free motion in abduction and adduction.

In the Cynomorpha, and even in the so-called "tailless" genus, Inuus, proper caudal muscles are present. In the limbs there is a levator claviculae which passes from the transverse process of the atlas to the acromion; a dorso-epitrochlearis, consisting of a muscular bundle detached from the latissimus dorsi near its insertion, and passing to the distal and inner end of the humerus, or even farther down; a scansorius, from the ventral edge of the ilium to the great trochanter, which sometimes becomes confounded with the glutoeus minimus; a special abductor ossis metacarpi quinti; and a peronoeus quinti digiti, arising from the fibula, between the peronoeus longus and brevis, passing behind the external malleolus, and sending its tendon to the extensor sheath of the fifth digit.

The extensor primi internodii pollicis and the peronceus tertius are absent in this, as in the preceding group.

The biceps femoris usually possesses only an ischial head, and the soleus arises only from the fibula. The flexor brevis digitorum arises partly from the tendon of the plantaris, where this passes over the pulley on the posterior surface of the calcaneal process to become continuous with the plantar fascia, and partly from the tendons of the long flexor. The transversus pedis is usually fully developed, but has only two heads of origin from the distal ends of the second and third metatarsals. The interossei pedis are just visible on the dorsal aspect of the foot, but none are, properly speaking, dorsal. None of them are penniform muscles arising from adjacent sides of the metatarsal bones; but they are attached, in pairs, to the plantar and lateral aspects of the metatarsal bones of the digits to which they appertain. They are inserted into the sesamoid bones, of which each digit has two, and into the bases of the proximal phalanges, and give off no distinct tendons to the extensor sheaths. Additional muscles may arise over the proximal ends of the metatarsal bones, and pass to the three fibular digits.

The interossei manus are very similar to those of Man, being divided into a dorsal and a palmar set, and sending slips to the extensor sheaths of the digits, without that complete subdivision which is seen in the Anthropomorpha,

There is a complete double set of extensors in the four ulnar digits of the manus, the extensor minimi digiti giving a tendon to the fourth digit, and the extensor indicis one to the third digit. The extensor ossis metacarpi pollicis gives a distinct slip to the trapezium, and thus precisely corresponds with the tibialis anticus, which has two tendons, one for the ento-cuneiform, and one for the metatarsal of the hallux. The flexor digitorum profundus and flexor longus pollicis are represented by one muscle, a slip from the ulnar side of the tendon of which usually goes to the pollex.

The tendons of the flexor perforans digitorum and flexor hallucis unite to form the deep flexor tendons of the pedal digits in very variable proportions. The flexor acccssorius is very generally present.

The anterior upper premolar has its outer cusp peculiarly modified and sharpened. The anterior lower premolar has the anterior margin of its crown prolonged and cutting, so that it works like as cissors-blade, against the posterior edge of the upper canine. In the upper jaw, the premolars have three roots; in the lower two. The molars in both jaws have four cusps connected by two transverse ridges. Sometimes there is "heel" behind the posterior ridge of the last lower molar.

The formula of the milk dentition is d.i. 2.2/2.2 d.c. 1-1/1-1 d.m. 2.2/2.2=20; and the anterior milk molar resembles the permanent premolars, while the posterior is like a permanent molar.

The permanent canines make their appearance before, or, at latest, contemporaneously with, the hindermost molar in both jaws. They are large and long, and are separated, by a well-marked diastema, from the outer incisor above, and from the first premolar below.

The Cynomorpha very generally possess cheet-pouchea, which serve as pockets for the temporary stowage of food. The stomach is usually simple, with a globular cardiac extremity and an elongated pyloric portion; but, in Semnopithecus and Colobus, the stomach is divided into three compartments, the middle of which is sacculated. A groove with raised edges leads from the cardiac end of the gullet to the middle compartment.

The caecum, though distinct, is relatively small, and has no vermiform appendage.

The liver varies much in the degree of its subdivision into lobes, being least divided in the Semnopitheci, and most in the Baboons. The innominate artery generally gives origin to both carotids, as well as to the right subclavian, the left subclavian arising directly from the arch of the aorta.

When laryngeal air-sacs are developed, they are not formed by dilatations of the lateral ventricles of the larynx, but a single sac, with a median aperture, is formed in the thyro-hyoidean space immediately beneath the epiglottis. This median air-sac is very large, extending down over the front of the neck, and sending processes into the axillae, in some Semnopitheci and Cynocephali. The right lung is usually four-lobed, the left two-lobed.

The kidney has only a single papilla. The posterior lobes of the cerebrum project beyond the cerebellum in all the Cynomorpha; they are shortest in the Semnopitheci, and longest in the Cynocephali. The principal sulci and gyri which are found in the human brain are always indicated; but the external perpendicular fissure is strongly marked. The posterior cornu of the lateral ventricle is large, and there is a strongly-marked hippocampus minor.

There is usually, if not always, a bone in the penis, which is provided with two special retractor muscles. The females are subject to a periodical turgescence of the sexual organs, sometimes accompanied by haemorrhage, and comparable to menstruation. The placenta is often bilobed.

 
     
 
 
     



     
 
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