THE BONES OF THE HEAD 163 



pression. The position of parts, then, is as follows: The globular process 

 forms the inner boundary of the nasal pit, and the lateral nasal process forms 

 its outer boundary, the optic or ocular depression lying on the outer side of 

 the lateral nasal process. In other words, the lateral nasal process hes 

 between the nasal pit internally and the optic or ocular depression externally. 

 The two nasal pits communicate widely with the primitive mouth or stomo- 

 daeum. Inferiorly the lateral nasal process is contiguous to the ventral 

 part of the maxillary process, from which it is at first separated by a groove, 

 called the oculonasal, naso-optic, or lachrymal sulcus, which extends from 

 the ocular depression to the nasal pit. This sulcus subsequently disappears, 

 but it indicates the position of the future lachrymal sac and nasal duct. The 

 lateral nasal process joins the maxillarj' process, and the two fuse with the 

 globular process. 



Fronto-Nasal Process. Parts developed from it. (i) Globular Process. — 

 Each globular process, as stated, consists of a core of cartilage, covered by 

 a connective-tissue investment. The cartilaginous core disappears, and 

 from the connective-tissue investment of each process the following parts are 

 developed: [a) The incisor or premaxillary portion of the superior maxilla; 

 (b) the anterior part of the palatal plate of the superior maxilla — that is to 

 say, the part in front of the incisor or premaxillary suture through means of 

 the nasal lamina : and (c) the portion of the upper lip, which corresponds to the 

 premaxilla. The portion of the mesial nasal process which lies between the 

 two globular processes gives rise superiorly to the dorsum of the nose, and 

 inferiorly to the lower and anterior part of the nasal septum, which part is 

 called the columella nasi. 



A prolongation of each globular process takes place in a backward direction 

 in the form of a plate. These two plates are called the nasal lamincs. At 

 first they are some distance apart, but they gradually come together, and 

 each forms the anterior part of the palatal plate of the corresponding superior 

 maxilla — that is to say, the part in front of the incisor or premaxillary 

 suture, and belonging to the premaxilla. 



(2) Lateral Nasal Processes. — Each of these, as stated, consists of a core of 

 cartilage, covered by a connective-tissue investment. The cartilaginous core 

 gives rise to the upper and lower lateral nasal cartilages. The connective- 

 tissue investment gives rise to the ala nasi, and the nasal and lachrymal 

 bones. 



First Visceral, or Mandibular Arches, and their Maxillary Processes. — 

 Simultaneously with the foregoing developmental changes, the mesoderm 

 of each mandibular arch is undergoing differentiation. From the dorsal or 

 proximal part of each mandibular arch a budding of its mesoderm takes place. 

 This outgrowth gives rise to the well-marked maxillary process, which is for 

 the most part membranous. 



Maxillary Processes. — ^The two maxillary processes grow in a ventral and 

 mesial direction, below the ocular depressions, and, as seen superficially, 

 on the primitive face, they Ue transversely, one on either side of the primi- 

 tive mouth. Their ventral or mesial extremities are widely separated from 

 each other, cind the mesial nasal process, with its two globular processes, lies 

 between them, forming the cephalic or superior boundary of the primitive 

 mouth. The lateral nasal process is contiguous superiorly to the ventral 

 part of the maxUlary process, the two being separated by the oculo-nasal, 

 naso-optic, or lachr\'mal groove, all as previously stated. Inferior to the 

 maxUlarj- process is the corresponding mandibular arch. 



The upper border of the maxillary process is joined by the lateral nasal 

 process, the oculo-motor or naso-optic groove becoming obliterated, and 

 being replaced deeply by the lachry-mal sac and nasal duct. The ventral 

 extremity of the maxillary process abuts against, and fuses with, the globular 

 process. As the result of this fusion between the maxillarj' process and 

 globular process, the external orifice (anterior nares) of the nasal pit of the 

 corresponding side (now developing into the nasal fossa) is cut off from 

 direct communication with the primitive mouth, but the nasal pit itself still 

 remains in free communication with that cavity. 



