DEVELOPMENT OF THE SKULL IN THE PIG. 



311 



condyloid foramen " (9), and then the " foramen lacerum posterius " (8). Crest-like, above 

 the foramen magnum and auditory mass, is the superoccipital cartilage (s.o.), ending 

 in front in a sinuous manner, being notched and bulged out by the lateral sinus 

 (/.r.). The ear-sac (an.) is an ovoidal flattened body, lying obliquely outwards and 

 backwards, with its bored and scooped face on the inner side. The blind recess under 

 the arch of the anterior canal is for the cerebellar process ; the antero-inferior spaces 

 are for the compound seventh nerve ; the meatus internus has a small cartilaginous 

 bridge in front of it, which passes upwards inside the canal for the portio dura. Between 

 the ear-sac and the small thick alisphenoid (al.s.), there is a large shallow fossa for the 

 Gasserian ganglion (5), and the space for the main part of the fifth nerve is merely the 

 great chink between these two parts — the alisphenoid and the ear-sac. Hence in the 

 Pig Ave see no " foramen ovale," and the " f. rotundum " has no distinctness from the 

 chink between the orbito- and alisphenoids. Most of the alisphenoid is spent in form- 

 ing the large " external pterygoid process," and its cranial part is small ; here it is not 

 the " ala major," as in Man. On the other hand, the " alae minores " of Man are re- 

 presented in the Pig by huge Avings of cartilage, that spread themselves from the nasal 

 to the auditory regions. This reversal in size of the anterior and posterior wings is like 

 what we see in the Lizard, &c., — unlike the Bird's skull in this respect, where the orbito- 

 sphenoids are aborted, the alisphenoids huge. As in the Lizard, the Mammalian 

 orbito-sphenoid has a postneural band, which encloses the optic nerve (2) in a complete 

 foramen : this is well developed in the Pig (Plate XXX. fig. 3, o.s. 2). In front of the 

 optic nerve the base of this orbital wing is continuous with the trabecular commissure 

 for some extent ; the greater part of the so-called presphenoid is, however, trabecular in 

 nature. The olfactory roof and wall extends backwards behind the septum, which 

 graduates into the presphenoid ; thus a large rounded notch exists on each side, and 

 the roof of the true olfactory region and floor of the rhinencephalon is soft ; through 

 this delicate tissue the olfactory filaments root downwards to the rudimentary upper 

 and middle turbinal septa (u.tb., m.th.). Between the nerve-fibrils cartilage is beginning 

 to appear, and thus a cribriform plate will be formed of secondary cartilage (fig. 3, cr.p.). 

 In front of the upper tvirbinal a rudimentary " nasal turbinal " (n.tb.) is formed by bending 

 inwards of the aliseptal cartilage. Lower down this cartilage turns inwards, and deve- 

 lops into the inferior or anterior turbinal (i.tb.), attached to which in front is the small 

 alinasal turbinal [al.th.). 



Fourth Stage. — Embryo of the Pig, from 2 inches 4 lines to 2 inches 6 lines in length. 



From dissections and sections of embryos not larger than the grub of the honey-bee 

 in the first, we come in this stage to specimens as large as a mouse. 



This is an excellent stage for morphological comparison, as tire skull may well be 

 placed side by side with that of the adult Osseous and Ganoid Fish, Amphibian and 

 Reptile, and with that of the ripe chick of the Common Fowl. It also corresponds very 

 closely in development with an early stage of the skull of Bala^na japonica, Lac, excel- 



