622 



CHORD AT A. 



two sides are pressed together to a single bone lying vertically 

 entirely within the nasal partition; the palatine and pterygoid are 

 forced backwards. The palatines contribute to the hard palate, 

 the pterygoids only exceptionally (Cetacea, many edentates); the 

 latter usually lose their independence and fuse with the nearest 

 bone of the base of the cranium, the basispheuoid (more accurately 

 witli a process of the basisphenoid, the lamina externa of the 

 pterygoid process, the pterygoid forming tlie lamina interna). 

 Thus the hinder sp)lienoid, lils;e the temporal, contains cranial and 

 visceral elements. 



In the vertebral column the cervical and the rib-bearing 

 thoracic vertebraj are always distinct, and the same, with the ex- 

 ception of the Cetacea and Sirenia, is true of lumbar, sacral, and 

 caudal vertebra;. Of sacrals there is one in all embryos, and 

 throughout life in the marsupials, elsewhere from two to five, 

 rarely, as in edentates, as many as thirteen. The number of ver- 

 tebras in each group is rather restricted. Thus, except in Brady- 

 piis tridactylus (0), Cholcepua lioffmanni and Manatus (0), the 

 number of cervicals is always seven. 



Of the appendicular skeleton the girdles are most interesting. 



The coracoid, which in mono- 

 ti'emes reaches the sternum, is 

 reduced in all other mammals to 

 a small coracoid process of the 

 scapula. More rarel_y the clavicle 

 is lacking (rapid runners); in 

 the nionotremes it extends to the 

 epistornum (fig. 048, CI, Ep); 

 elsewhere it aj^pears to articulate 

 with the sternum, in reality by 

 the intervention of interarticular 

 cartilages (once regarded as a 

 rudimentary episteruum, now 

 called preclavia?). In the pelvis 

 all three elements are fused to a 

 single OS innominatum ; pubis and 

 ischium unite ventrally with each other, enclosing between them 

 the obturator foramen (fig. 655). The pubes of the two sides 

 unite by a symjihysis which can extend back to the ischia. 



Since the nuimmals in general are distinguished from other 

 vertebrates by their intelligence, the brain is characterized by the 

 size of cerebrum and eerebellnm (fig. 049). In contrast to birds 



Fig. 648.— Sternum and shoulder girdle 

 of OrnithnrhyncJuis paradnxits. (E'rom 

 Wiedershehn.) CU clavicle; Cn. Cri\ 

 coracoid; Ep, episternum; G, glenoid 

 fossa for liumerus: .S, scapula; N7, 

 uianubriuni sterni (anterior element 

 of sternum). 



