336 



THE CAT. 



[CHAP. x. 



Fig. 153. OUTLINE OF THE HEAD AND NECK OF AN EMBRYO 



PlG, TWO-THIRDS OF AN INCH IN LENGTH, SEEN LATERALLY. 



MAGNIFIED SEVEN DIAMETERS. 



the opposite side toform 

 the lower jaw, while 

 a process grows for- 

 ward and upward from 

 the more proximal 

 part of each first 

 visceral arch, such 

 growth, termed the 

 maxillary process (Fig. 

 152, mps) t laying the 

 foundation of the up- 

 per jaw. The two 

 maxillary processes do 

 not, however, join to- 

 gether in front, hut 

 both join a median 

 down growth, termed 

 the naso-frontal process 

 (Fig. 152, *). This 

 last-named process de- 

 scends from the front 

 end of the floor of 

 the incipient cranium, 

 and has on each side 

 of it one of the two 

 depressions which are 

 the incipient olfactory 

 sacs. Its lower end 

 forms the middle of 

 the front of the upper 

 jaw, while the max- 

 illary processes which 

 unite with its distal 

 end, on each side,form 

 the sides of the upper 

 jaw. The interval left 

 on each side (above 

 the junction of the 

 naso-frontal and max- 

 illary processes,) forms 

 the nasal passage, and, 

 in part, the lachrymal 



Fig. 154. THE SKULL OF THE SAME EMBRYO (IN ITS INCIPIENT 

 STAGE OF DEVELOPMENT), SEEN FROM BELOW. MAGNIFIED 

 TEN DIAMETERS (VENTRAL ASPECT). 



The following letters indicate the same parts in whichever of the above figures they occur, or in 

 both figures : 



c 1 to c 5 . The five divisions of the young brain. 

 a. The eye. 

 n. The nose. 

 m. The mouth. 

 tr. Cartilage of the trabeculse. 



ctr. Cornua trabecularum. 

 pn. Pre-nasal cartilage. 



ppg. Pterygo-palatine cartilage. 



mil. The mandibular arch, with Meckel's carti- 

 lage. 



te. First visceral cleft, which becomes the tym- 

 pano-Eustachian passage. 



au. The auditory vesicle. 

 hy. The cerato-hyoid arch. 

 tr (1 to 4). The branchial bars and clefts. 

 thh. The thyro-hyoid. 

 py. The pituitary fossa. 



c/i. The notochord in the cranial basis, sur- 

 rounded by the investing mass (iv). 

 VII. Facial nerve. 



IX. Glosso-pharyngeal. 



X. Pneumogastric. 

 XII. Hypo-glossal. 



