208 ANATOMY OF VERTEBRATES. 



In the Ornithorhynchus one olfactory nerve quits each rhincn- 

 cephalon and escapes from the skull by a single foramen at the 

 fore part of the prefrontal plate : it divides on entering the nasal 

 cavity into septal and turbinal branches. The membrane re- 

 ceiving the former is supported wholly on a bony plate : the 

 turbinals are partly bony, and partly gristly : a prenasal ossicle is 

 formed in the forepart of the nasal septum. 



The olfactory nerves in the Echidna are extremely numerous, 

 and the cribriform plate is large and encroaches upon the fore 

 part of the cranial cavity as a convex protuberance. The ethmo- 

 turbinals are of corresponding size, composed of a series of vertical 

 processes which expand and subdivide as they pass toward the floor 

 of the very long nasal passage. I have shown the lateral expanse 

 of these turbinals by a horizontal section in No. 1707, XLIV. p. 318. 



The olfactory nerves and the osseous cavities and laminre 

 destined for the protection and support of the pituitary membrane 

 offer a remarkable proportional development in all the Marsupials, 

 and more especially in the Insectivorous and Carnivorous tribes. 

 Certain species of Kangaroo, of the subgenus Osphranter, Gould, 

 remarkable for their acuteness of smell, have the turbinated bones 

 so large that the lateral expansion of the nasal cavity forms a 

 marked feature in the skull. The characters of the osseous 

 parts of the nasal cavity, in this order, are given in vol. ii. p. 348. 

 Through the defective ossification of the palate the convolutions 

 of the inferior turbinals are visible in the dry skull at that part ; 

 e.g. in Perameles layotis (vol. ii. fig. 222) and in Thylacinus. In 

 the latter marsupial the fine lacework perforation of the inferior 

 turbinals is well shown. 



In the Hare the inferior turbinal is large, longitudinally la- 

 mellate, and shows in well-injected specimens the highest degree 

 of vascularity : the complexity of its medial or septal surface 

 contrasts with the simplicity of that in Felines. The ethmotur- 

 binals are divided into three principal lamellrc : the nasal cavity 

 is long but narrow : the maxillary sinus is small. In the Agoutis 

 the nasal chamber is more expanded : the ethmoturbinals which 

 consist each of four rather short longitudinal lamella, are divided 

 from the maxillo-turbinals by a protuberance from the mesial 

 wall of the large maxillary sinus : there is a small ' Jacobsoii's' 

 process from the premaxillary at the lower and fore part of the 

 nasal cavity. In the Paca ( Ccdogenys) the olfactory cavity ex- 

 tends backwards beneath the rhinencephalic one. In the Porcu- 

 pines through the enormous development of sinuses from the 

 olfactory cavity it extends backward beyond the rhinencephalic 



