PRIMORDIAL CRANIUM OF THE CAT 339 



the olfactory fenestra through the sinus between the crista 

 semicircularis and ethmoturbinal I (p. 335). Although at this 

 stage the cartilaginous parts fail to meet in forming a medial 

 wall for the inferior portion of the lateral recess, the soft parts 

 which stretch between ethmoidal I, the crista semicircularis and 

 the floor shut off this part of the recess from the common meatus 

 of the nose and convert this part of the cavity into a blind pocket. 

 Similarly, the entrance from the common meatus into the re- 

 cessus lateralis between ethmoidal I and crista semicircularis 

 is very broad, as shown in the models, but by the presence of the 

 soft parts over these elevations, it is reduced to a narrow fis- 

 sure, the hiatus semilunaris of later stages. The lateral recess 

 is incompletely subdivided into dorsal and ventral rooms, re- 

 cessus lateralis superior and recessus lateralis inferior, by a 

 slight frontal ridge springing from the lateral surface of ethmo- 

 turbinal I, and by an oppositely placed ridge of the lateral wall 

 of the recess (fig. 27) . The superior lateral recess opens into the 

 common meatus of the nose through the dorsal part of the hiatus 

 semilunaris. Within it are two antero-posterior, curving ridges 

 of the mucosa, one upon the roof, the other on the lateral w^all. 

 Each includes a condensation of the mesenchyma which is in 

 contact, but apparently not continuous by any transitional zone, 

 with the cartilaginous wall. These ridges separate three out- 

 pocketings of the recessus lateralis superior, a lateral, a superior 

 and an inferior groove (fig. 27). The recessus lateralis inferior 

 is incompletely walled medially, as already explained. It 

 lodges a blind sac of mucosa which conmiunicates with the 

 connmon meatus through the ventral part of the hiatus 

 semilunaris. 



^ Posterior division. (Pars ethmoturbinalis) . This region of 

 the dorsal part of the lateral nasal wall corresponds to the 

 antorbital plane of the exterior. It is characterized by the 

 presence of the bases of the ethmoturbinals. Ethmoturbinal I 

 appears in the model as a massive irregular ridge, extending 

 dorso-ventrally on the lateral nasal wall at the caudal margin 

 of the entrance into the recessus lateralis (fig. 13). Anteriorly, 

 the process goes over into precartilage in the form of a broad, 



