DEVELOPMENT OF THE SKULL IN THE PIG. ; 3a 
place in the little auditory ossicles is too small to require special notice. The mandibular 
rami (Plate XX XVIL. 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 
Fiowrr’s work, ‘An Introduction to the Osteology of the Mammalia, 1870, p. 172, 
and also in Professor Huxtey’s ‘ Anatomy of the Vertebrated Animals,’ 1871, p. 368. 
SUMMARY. 
The most important results of the present investigation may be stated as follows :— 
1. Ina 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 bya rounded end immediately behind the pituitary body. 
(2) On each side of the notochord, but below it, a cartilaginous plate, which in front 
ends by a rounded extremity on a level with 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 Raruke. 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 prenasal 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 isa 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. 
(f) 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 
