Olfactory Apparatus in Dog, Cat and ^lan 33 



only, Scarpa and subsequent authors were justitied in their conclusions 

 that the nerve bundles form a plexus in this region. But upon a micro- 

 scopical examination after diiferential staining, it is found that the 

 nerve bundles do not anastomose. 



This plexiform appearance is due, not to a joining of nerve bundles, 

 but rather to the ramification of the blood vessels and to the arrange- 

 ment and abundance of the connective tissue which surrounds these 

 vessels and nerves (Figs. 24, 27). The nerves have been traced in these 

 cords of connective tissue. As shown in the drawing and photograph, 

 the}^ pass almost vertically through this to the foramina of the cribri- 

 form plate without anastomosis or the formation of a plexus (Figs. 

 24, 27). 



There is but little appearance of a plexus upon the nasal septum 

 (Figs. 25, 26), and the picture of Scarpa (Fig. 10) is much more 

 accurate than are those of Leveille. Figs. 13, 14, 24 to 27 show 

 strikingly that there is a marked difference in the plexiform appear- 

 ance of the lateral wall and septum. In both cases, especially upon 

 the septum, there is a crossing and recrossing of nerves, but focusing 

 shows that these do not join. There is, however, some slight joining of 

 the smaller nerve bundles near their origin (Figs. 25, 26). 



All authorities on comparative anatomy, wherever the subject is dis- 

 cussed, speak of a plexus of the olfactory bundles. But there is no 

 such marked appearance of this in dog and cat as that found in man. 

 It looks as if the conditions in man had been interpreted for mammals 

 without adequate investigation. Whenever there is an appearance of a 

 plexus, it has been found to be merely a crossing of nerve bundles. 



The Olfactory Bulb. 



The olfactory bulb has been descriljed Ijy various workers as consisting 

 of from two to seven layers, according to the subdivisions made l)y these 

 investigators. 



Golgi, 1875, describes three layers, olfactory fibers, mitral cells and 

 nerve bundles of the olfactory tract. Van Gehuchten and Martin, 1891, 

 also describe three main layers. In this paper we are concerned only 

 with the olfactory fibers, the glomeruli and mitral cells ; we will not 

 enter into the discussion beyond this. 



Van Gehuchten and Martin, 1891, worked on the dog and the cat, 

 both adult and young animals, also the rabbit, rat, and mouse. The 



