COMPARATIVE ANATOMY OF THE MAMMALIAN ORGAN OF JACOBSON. 247 



length of the canal is one of the points in which we have an advance on the Chiropterus 

 condition. The other main points of difference are due to a less degree of development 

 of the organ in the hedgehog, and a greater of the bony tissues. Though the naso- 

 palatine canal passes up very obliquely, it is supported by cartilaginous walls almost 

 exactly as in Miniopterus, and unquestionably of the same nature. Fig. 23, which repre- 

 sents a section of the snout of the hedgehog cut slightly obliquely, shows on the one side 

 the naso-palatine canal almost surrounded by cartilage. The upper and inner corner of 

 the canal is really the continuation of Jacobson's duct. If this figure be compared with 

 fig. 19 the close agreement of the two will be at once manifest. In the hedgehog the 

 nasal floor cartilage is represented only by the inner part above, and by the feebly 

 developed outer wall of the naso-palatine canal. In the other side of fig. 23 the section 

 passes through the point where the naso-palatine canal opens into the nasal cavity, and 

 Jacobson's duct is likewise seen opening into the nasal cavity at this point. Jacobson's 

 cartilage is here represented in two portions — a lower small concave portion which lodges 

 the duct of Jacobson, and a small upper plate which is the continuation of the nasal floor 

 cartilage proper. This section may be compared with fig. 20 of Miniopterus. Almost 

 immediately beyond this plane the two portions of Jacobson's cartilage unite, and we 

 soon get on section an appearance like fig. 24, with the organ well protected by a large 

 cartilage. This section may be seen to agree fairly closely with fig. 21 from Miniopterus, 

 the outer nasal floor cartilage being unrepresented in the hedgehog. 



Carnivora. — As a result of Klein's work we have a very complete account of the 

 organ and its relations in one of the members of this order, the dog. Though the 

 arrangement of the cartilages in the dog is quite characteristic of the carnivorous type, 

 their development indicates some degree of degeneration, and in the cat we have a much 

 better representative of the order, as the cartilages here attain their full development. 



As in the hedgehog we have an advance upon the Miniopterus condition, so in the 

 cat we have a further stage in the specialisation of the same type ; and the hedgehog 

 condition stands almost intermediate between the primitive bat condition and the more 

 specialised condition of the cat. 



In the cat we have a very long naso-palatine canal supported by cartilaginous walls 

 as in the hedgehog. The mutual relations of the canal and its cartilaginous walls are 

 well shown by Klein in his paper on the organ in the dog, and the condition in the cat 

 is essentially similar. In both the bat and hedgehog the organ was seen to open into the 

 nasal cavity as well as into the naso-palatine canal ; in the cat the duct of the organ 

 opens into the canal well in advance of the posterior end of the canal, and thus only 

 communicates with the nasal cavity indirectly by means of the naso-palatine canal. In 

 fig. 25 the naso-palatine canal is supported by cartilage almost exactly as in the hedge- 

 hog ; the nasal floor cartilage is, however, much better developed. Fig. 26 represents 

 lacobson's duct separating off from the canal, and already the inner part of the cartilage 

 — the anterior process of Jacobson's cartilage — is seen distinct from the outer portion or 

 the process from the outer nasal floor cartilage. In fig. 27 we see the whole four 



VOL. XXXIX. PART I. (NO. 8). 2 P 



