BETWEEN TYPICAL REPTILES AND OTHEB ANIMALS. 187 



generally rounded and smooth. The neural arch in the early 

 part of the back is usually directed forward in mammals, as it is 

 in the back of Iguana ; and in the lumbar region of mammals the 

 neural spine is usually quadrate and erect as in the back of 

 Monitor. 



The tail in long-tailed mammals like the Marsupials and Mono- 

 tremes rarely includes more than twenty vertebrae, except in 

 Paradoccurus, while in Monitor there may be more than 100. 

 The transverse process is more persistently developed in the 

 mammalian caudal region than in Lizards ; in Lizards the neural 

 arch is the persistent part. 



The riba of Lizards appear to consist of a variable number of 

 parts determined by the state of the specimen as fresh or dry. 

 Taking three as the normal number in Iguana, the same number 

 of parts may be seen in a few ribs of some Porpoises ; and in 

 OrnitliorliyncJius there is a long unossified element between the 

 dorsal and sternal ribs. 



The pectoral girdle resembles that of a Monotreme in con- 

 sisting of scapula, coracoid, clavicle and interclavicle, while the 

 mammal differs in the coracoids not meeting the sternum, and in 

 those bones being divided by two others not seen in Lizards, which 

 are named the epicoracoids. The episternum or interclavicle is a 

 T-shaped bone in both, which carries the clavicles [often] on its 

 cross bar in front, and in the mammal meets the proximal end of 

 the sternum behind, while in the Lizards it extends mesially 

 down the front of the large lozenge-shaped sternum. The ends 

 of the cross bar in some Lizards unite with a process of the 

 coracoid ; in the mammal they extend along the clavicle nearly 

 to the acromion process of the scapula. The scapula of the Mono- 

 treme, with its anterior lateral acromion-process, situate as in 

 Cetaceans, is like the scapula of Iguana, where, however, the pro- 

 cess is much longer — though in Monitor the coracoid unites with 

 the whole side of the scapula, so that there is no true acromion. 

 In the Monotreme the clavicle extends to this process ; in the 

 Lizard it extends beyond it to the suprascapula. The massive 

 coracoid of CJiamceleon or Hatteria is more like that of Mono- 

 tremes than the emarginate bones of ordinary Lizards. 



The diamond-shaped sternum of the Pike- Whale is relatively 

 smaller than in Lizards, and has different relations ; and, except 

 in Chameleons, it is not usual for Lacertians to have the sternum 



