THE CKANIAL SKELETON. 19 



The basilar plate does not extend under the floor of the 

 pituitary fossa, but the cartilage is continued forwards on 

 each side of this, in the foi-m of two bars, the trabeculce 

 cranii. In front of the fossa, the trabeculse reunite and end 

 in a broad plate, usually bifurcated in the middle line — the 

 ethmovoinerine plate. 



On each side of the posterior boundary of the skuU, 

 the basilar cartilage grows upwards, and meets with its 

 fellow in the middle line, thus circumscribing the occipital 

 foramen, and furnishing the only cartilaginous part of the 

 roof of the skull; for any cartilaginous upgrowths which 

 may be developed in the more anterior parts of the skull 

 do not ordinarily reach its roof, but leave a wide, merely 

 membranous space, or fonianelle, over the greater part of 

 the brain. 



Before the sktdl has attained this condition, the organs 

 of the three higher senses have made their appearance in 

 pairs at its sides ; the olfactory being most anterior, the 

 ocular next, the auditory posterior (Fig. 4). 



Each of these organs is, primitively, an involution, or sac, 

 of the integument ; and each acquires a particidar skeleton, 

 which, in the case of the nose, is furnished by the ethmo- 

 vomerine part of the skull; while, in that of the eyes, it 

 appertains to the organ, is fibrous, cartilaginous, or osse- 

 ous, and remains distinct from the skull. In the case of the 

 ear, it is cartilaginous, and eventually osseous : whether 

 primitively distinct or not, it early forms one mass with the 

 skull, immediately in front of the occipital arch, and often 

 constitutes a very important part of the walls of the fully- 

 formed cranium. 



The ethmovomerine cartilages spread over the nasal 

 sacs, roof them in, cover them externally, and send down 

 a partition between them. The partition is the proper 

 ethmoid, the lamina perpendicularis of human anatomy ; the 

 posterolateral parts of the ethmovomerine cartilages, on 

 each side of the partition, occupy the situation of the pre- 

 frontals, or lateral masses of the ethmoid of human anatomy. 

 The ingrowths of the lateral walls, by which the nasal 



