56 Mammalia. Monotremata. 



and terminating towards the snout, as expanded spatulate processes. 

 - In both species theCoronoid process and the angle of the jaw are rudi- 

 mentary. Echidna has a well developed cribriform plate, but in Orni- 

 thorhyncus the olfactory nerve escapes by a single foramen (Sauroid 

 affinity). Lastly, we may note the lony falx found in Ornithorhyncus 

 only of this order (and rarely foand in other orders) attached internally 

 to the middle line of the coalesced parietals. 



The Vertebral column. The pleurapophyses in the Cervical region 

 retain their individuality. In Ornithorhyncus (but not in Echidna) 

 hypapophyses are present in the cervical vertebrae ; and are bifur- 

 cated in Atlas. The haemapophyses-'' of the first six Dorsal 

 vettebrse are ossified, and have cartilage interposed between them 

 and the pleurapophyses, f as in the Crocodile : the rest of tjie haema- 

 pophyses are cartilaginous, and overlap each other. A small tubercle 

 defines the neck of the Rih save in the last four, but save in the first 

 and second, the Ribs do not articulate with the diapophyses, but only 

 with the centra of the vertebrae helow the neuro-central suture, the 

 reverse of what occurs in the higher Mammals. The Frmsternum or 

 Manubrium is divided by an intervening layer of cartilage into two 

 parts : of these the posterior, or plcur-osteon, receives the haemapo- 

 physes of the first and second Ribs ; while the anterior, or pro-osteon, 

 is in relation with the Coracoids and Epicoracoids superiorly, and 

 with the body of the large T-shaped Inter-claviele[^/s^^r;^^^w, Owen] 

 (on which the Clavicles are supei-poscd) inferiorly. In Ornithorhyncus 

 the Sacral vertebrae remain permanently separated. In Echidna the 

 fluid central part of the intervertebral substance fills a more definite 

 cavity than in higher Mammalia ; and none of the Cervical vertebrae 

 have zygapophyses except the atlas. The (7(f)!w^<?/ vertebrae seldom have 

 haemapophyses articulated to the vertebral interspaces, as in many 

 Marsupials. The spinal nerves usually j9e;/oraif^ the neurapophyses. J 



The Scapular Arch and Appendages. The Scapular Arch is 

 arranged according to the type of the Sauropsida. The Scapula is 

 long, and sabre-shaped. The Coracoid, which in this order alone of 

 Mammalia attains its normal proportion, is developed as a distinct 

 bone, and extends from the Scapula to the Interclavicle, and also to 



* Sternal Eibs. f Vertebral Kibs. 



X The same arrangement obtains in Bovida?, and Tapir. 



The Epicoracoid is a flat shield-like plate of bone, placed in front of the 

 inner end of the Coracoid, the rounded inner border of which passes beyond the 

 median line, overlapping the corresponding bone of the opposite side. Floioer. 



