PRIMORDIAL CRANIUM OF THE CAT 333 



Just ventrad of its junction with the anterior part of the paries 

 nasi it is crossed by the naso-lacrimal duct. The caudal margin 

 of the lamina is free and is separated by a wide interval from 

 the paraseptal cartilage. 



Behind the anterior transverse lamina, the tear duct lies upon 

 the most ventral part of the paries nasi and is further supported 

 by a cylindrical processus maxillaris anterior of the latter (figs. 

 3, 13, 30) directed forward. At this place the os maxillare over- 

 laps the nasal capsule and, in the model, hides from view the 

 maxillary process and tear duct. 



The cartilago paraseptahs (figs. 2, 3, 13, 28, 29), scroll-formed 

 in adaptation to Jacobson's organ, hangs from the septum nasi 

 below the level of the plane of the fenestra basaUs. It is uncon- 

 nected with other parts of the nasal skeleton. The medial half 

 of each cartilage hes in a sagittal plane applied against the ven- 

 tral part of the septum. The lateral half is rolled dorsally to 

 form a gutter lodging the vomero-nasal organ. The cephalic 

 margin is free and straight; the caudal pointed. The long axis 

 of Jacobson's cartilage extends from behind cephalo-ventrad, 

 the caudal extremity lying at the level of the basal window, the 

 cephahc end reaching a position ventrad of the plane of the an- 

 terior transverse lamina. At this stage the paired naso-palatine 

 cartilage is represented by a stretch of prochondral tissue upon 

 the lateral side of each incisive duct.^ The U-shaped beginning 



kandl the medial and lateral limbs of the ventro-lateral process of the septal 

 cartilage. The incisive duct is partly enveloped on its lateral side by a trough- 

 shaped nasopalatine cartilage, which reaches from a spot near the oral end of the 

 duct, to the level of the entrance of the duct of Jacobson's organ. The last named 

 canal is surrounded completely by a cartilaginous tube which, as it ascends 

 toward the cavum nasi, gradually loses its dorsal wall and becomes continuous 

 with the anterior extremity of the paraseptal (Jacobson's) cartilage. The car- 

 tilage of Jacobson's duct lies medial of the process of the lamina transversalis 

 anterior; neither it nor the nasopalatine cartilage is joined with the processes of 

 the anterior transverse lamina. 



■* The paraseptal cartilage in embryos of 70 mm. presents an anterior process, 

 continuous with the cartilage of the duct of Jacobson's organ, and continues 

 posteriorly into a slender cartilaginous paraseptal rod. The latter lies against 

 the side of the ventral edge of the vomer and extends to the floor of the posterior 

 cupola, the lamina transversalis posterior with which it is directly continuous. 



