1873.] 



of the Skull in the Pig. 



403 



I have added young pigs at birth, and have taken as the last stage the 

 skull of a half-grown individual. 



The most important results of the present investigation may be stated 

 as follows : — 



1. In a pig-embryo, in which the length of the body did not exceed 

 two thirds of an inch, and four postoral clefts were present, the cranio- 

 facial skeleton was found to consist of : — (a) the notochord, terminating 

 by a rounded end immediately behind the pituitary body. 



(b) On each side of the notochord, but below it, there is a cartilaginous 

 plate, which in front ends by a rounded extremity on a level with the 

 apex of the notochord, while behind it widens out and ends at the free 

 lower margin of the occipital foramen. These two plates, taken together, 

 constitute the " investing mass " of Bathke. In this stage they send up 

 no prolongations around the occipital foramen; in other words, the 

 rudiment of the basioccipital exists, but not of the exoccipital or super- 

 occipital. 



(c) The large oval auditory capsules lie on each side of the anterior 

 half of the investing mass, with which they are but imperfectly united : 

 there is no indication of the stapes at this stage. 



(d) The trabecular or first pair of prseoral visceral arches inclose a 

 lyre-shaped pituitary space ; they are closely applied together in front of 

 this space, and, coalescing, give rise to an azygous prsenasal rostrum. 

 They are distinct from one another and the investing mass. 



(e) The pterygopalatine or second pair of visceral arches lie in the 

 maxillo- palatine processes, and are therefore subocular in position. 

 Each is a sigmoid bar of nascent cartilage, the incurved anterior end 

 of which lies behind the internal nasal aperture, while the posterior 

 extremity is curved outwards about the level of the angle of the mouth. 

 The pterygo-palatine cartilages are perfectly free and distinct from the first 

 praeoral and from the first postoral arch. 



(/) The mandibular or first pair of postoral visceral arches are stout 

 continuous rods of cartilage which lie in the first visceral arch behind 

 the mouth. The ventral or distal ends of these arches are not yet in 

 contact ; the dorsal or proximal end of each is somewhat pointed and 

 sharply incurved, pushing inwards the membrane which closes the first 

 visceral cleft and is the rudiment of the membrana tympani. 



(g) The hyoid or second pair of postoral arches are in this stage 

 extremely similar to the first pair, with which they are parallel. They 

 are stout sigmoid rods of cartilage, which are separated at their distal 

 ends, present an incurved process at their opposite extremities, and are 

 not segmented. 



(Ji) The ihyro-hyal or third postoral arches, which correspond with 

 the first branchial of the branchiate vertebrata, are represented by two 

 short cartilaginous rods which lie on each side of the larynx. 



(i) The olfactory sacs are surrounded by a cartilaginous capsule, which 



