XIII 



PHYLUM CHORDATA 



525 



bound the orbit behind ; the upper one is formed from the parietal 

 (par). The facial region is comparatively short. The premaxillae 

 (p. max) are not greatly developed. There are distinct paroccipital 

 processes (p. oc.). The periotic and tympanic are ankylosed 

 together, but not to the squamosal. The tympanic (ty.) forms a 

 bulla with a spout-like prolongation. 



In the Proboscidea (Fig. 1169) the bones of the skull are of 

 enormous thickness, the inner and outer tables being separated by 

 extensive air-cells. The sutures are early obliterated. Paroccipital 

 and postglenoidal processes are absent. The tympanic forms a 

 large, rounded auditory bulla ; but the external auditory meatus 

 is bounded chiefly by the post-tympanic process of the squamosal. 

 The mastoid portion of the periotic does not appear on the surface. 

 The orbit is not completely separated by bone from the temporal 

 fossa. The nasal aperture is situated far back, and looks upwards 

 and forwards almost as in the skull of some *.$ 



of the Cetacea. The chief characteristic of 

 the mandible is -its prolongation forwards 

 into a spout-like process at the symphysis. 



In the Ungulata vera the scapula (Fig. 

 1170) is never very broad ; the spine is 

 usually near the middle. Neither the acro- 

 mion nor the coracoid process is very pro- 

 minent ; sometimes, as in the Horse, the 

 former is absent. A clavicle is never 

 present. In the Ruminants, as in some 

 other Mammals, the vertebral portion of 

 the scapula remains cartilaginous, forming 

 the so-called supra-scapular cartilage (ss). 

 In Pigs and some Perissodactyles, though 

 there is no acromion, there is a triangular 

 process about the middle of the spine. 



The humerus is short and stout, the 

 radius always well developed, the ulna in 

 some (Pigs, Hippopotami, Tapirs, and FIG. mo. Right scapula of 



T->I- \ 11 i i i Red Deer (Cervus elaphus) 



Rhinoceroses) well developed, in others (the a . acromion ; /. prescapuiar 

 Horses and the Ruminants) incomplete. [^/^Tgg&'SSg^ 



The first digit is always absent. There f mpe p r f ^ P S fle ^ u ; P S: 

 is never a centrale. The trapezoid and scapular portion. (After 

 magnum unite in most of the Ruminants. 



In the Perissodactyla the third digit in both the fore- and hind- 

 foot is symmetrical in itself. In the Rhinoceroses the second and 

 fourth are also present, and in the Tapirs (Fig. 1171) the fifth of 

 the fore-foot is developed as well. The Horses (Fig. 1172) present 

 the greatest reduction in the number of the digits observable in 

 any Mammal, the third being the only functional digit in each 

 foot. Its elongated metacarpal or metatarsal (sometimes called 



VOL. II K K 



