96 



SMELL, TASTE, ALLIED SENSES 



111 all these higher vertebrates the olfactory organ proper 

 corresponds to the lateral component of the pair of 

 organs in the lower forms and the vomero-nasal organ 

 to the median member of this group (Fig. 23). 



3. Histology. The vomero-nasal organ of the dog 

 and the cat, as described by Read (1908), is a tubular 



organ whose transverse 

 section is circular in out- 

 line near its opening 

 and crescentic or kidney- 

 shaped throughout its 

 greater extent. Its median 

 wall may be two to three 

 times as thick as its lateral 

 wall. This thickened por- 

 tion, which has been 

 observed by numerous 

 workers in a variety of 

 mammals, is similar in 

 cellular composition to the 

 olfactory epithelium of 

 the nose and is in strong 

 contrast with the lateral 

 thin wall which resembles respiratory nasal epithelium. 

 Read has shoMoi that the vomero-nasal organ of the cat 

 and the dog is like the olfactory region of the nose in that 

 it receives nerve fibers from two sources, the olfactory 

 nerve and the trigeminal nerve. 



As early as 1892 von Brunn showed that the sense 

 cells of the vomero-nasal organ of the sheep were con- 

 nected with nerve fibers in exactly the way they were in 

 the olfactory region proper and he assumed, probably 



Fig. 22. — Transverse section of the head 

 of a snake embryo (Agkistrodon) showing 

 the nasal canal proper (n) and the large 

 vomero-nasal (v) organ opening on the 

 roof of the mouth. Preparation by Mr. 

 F. B. Manning. 



