DEVELOPIklENT OF THE SKULL IN TlIE PIG. 



327 



place in the little auditory ossicles is too small to require special notice. The mandibular 

 rami (Plate XXXVII. fig. 3) are quite distinct from each other at present: they are 

 large deep bones, with a small notch between the coronoid and articular regions ; the 

 latter is somewhat pyriform, with the narrow end inwards ; the angular region is flat, 

 with a round outline and a thick rugose edge. 



Ninth Stage. — The Skull in Adult Pigs. 



The further changes that take place in the Pig's skull are mainly increase of size and 

 extensive ankylosis. Besides referring the reader to the actual object, I may mention 

 that a short and useful account of this type of cranium will be found in Professor 

 Flowek's work, 'An Introduction to the Osteology of the Mammalia,' 1870, p. 172, 

 and also in Professor Huxley's ' Anatomy of the Vertebrated Animals,' 1871, p. 368, 



SUMMAEY. 



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. 



{h) On each side of the notochord, but below it, a cartilaginous plate, which in front 

 ends by a rounded extremity on a level Avith the notochord, whilst 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 Eathke. In this stage they send up no 

 prolongations around the occipital foramen ; in other words, the rudiment of the basi- 

 occipital exists, but not that of the exoccipital nor superoccipital. 



{c) The large oval auditory capsules lie on each side of the anterior half of the in- 

 vesting 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 preoral visceral arches enclose a lyre-shaped pitui- 

 tary 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 pterygo-palatine 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 interior nasal aperture, 

 while the posterior extremity is curved outwards at about the level of the angle of the 

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

 preoral and the first postoral arch, although developed in a process of the latter, and 

 are therefore secondary arches. 



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

 rods of cartilage, which lie in the first visceral arch behind the mouth. The ventral or 



