THE PHAEYNX. 



553 



By this telescoping of the visceral arches a deep cleft is 

 formed at each side of the neck, extending round to its ventral 

 surface, and dividing the pharyngeal region from the trunk. 

 This cleft, which presents a certain resemblance to the opercular 

 cavity of a tadpole, is the sinus prascervicalis (Fig. 240, su) ; it 

 ultimately becomes obliterated by fusion of its anterior and pos- 

 terior walls. 



3. The Upper Lip and the Palate. 



The fronto-nasal process consists, as already described, of a 

 median area (Fig. 240, FP), and two lateral lobes, the processus 



OD 



BR.2. 



FIG. 240. The head and neck of a Human Embryo thirty-two days old, seen 

 from the ventral surface. The floor of the mouth and pharynx has been 

 removed. Cf. Fig. 205, which is an outline figure of the same embryo. 

 (From His.) x 12. 



BR.l, first branchial arch. BR.2, second branchial arch. EB, membrane closing 

 the hyoinandibular cleft, which afterwards becomes the tympanic membrane. FC, pro- 

 cessus globularis. FP, median part of fronto-nasal process. HM, hyomandibular 

 poncli. HY, hyoid arch. LG, lung. LR, larynx. MN", mandibular arch. MX. 

 maxillary arch. OD, eye. OK, mouth of olfactory pit, or external nostril. PT, 

 pituitary body. SU, sinus prascervicalis. 



globulares, FC. The processus globulares form the inner lips 

 of the nasal grooves, which connect the olfactory pits with the 

 mouth, and of which the outer lips are formed by the inner 

 edges of the maxillary arches, MX. By fusion of their inner and 

 outer lips, the nasal grooves become converted into the posterior 



