XIII 



PHYLUM CHORDATA 



519 



bones. There are enormous pre- 

 maxillae in the Dugongs. ThS 

 mandible has a well-developed 

 ascending ramus and coronoid 

 process (cp.). 



The scapula of the Sirenia is 

 much more like that of the ter- 

 restrial Mammals than is that of 

 Cetacea, but is nearer that of 

 the Seals ; it is narrow and 

 curved backwards. The spine 

 is situated about the middle ; 

 the acromion is directed down- 

 wards. The coracoid is fairly 

 well developed, and of a conical 

 shape. The clavicle is absent, 

 as in the Cetacea. The skeleton 

 of the arm also departs less 

 from the ordinary Mammalian 

 type than in the Cetacea. The 

 radius and ulna are ankylosed 

 at their extremities. The car- 

 pus has seven bones in the 

 Manatee : the pisiform is absent. 

 In the Dugong coalescence takes 

 place between the carpal bones, 

 so that the number of ossifica- 

 tions is reduced in the adult. 

 There are five digits, all of which 

 possess the normal number of 

 phalanges. 



The pelvis is represented by 

 a pair or more of vestiges 

 widely separated from the spinal 

 column, and having a vertical 

 position : they probably repre- 

 sent the ilia. 



Skeleton of the Ungulata. 

 In general, the centra of the 

 Ungulata are more or less dis- 

 tinctly opisthoccelous. The 

 odontoid process of the axis (Fig. 

 1165) has a peculiar spout-like 

 form in the majority of the Rumi- 

 nants, and in a less marked 

 degree in the Horses and Tapirs : 

 in the Chevrotains, the Pigs, and 



