(ESOPHAGUS OF A COMMON MACAQUE. 29 



contrasts greatly with the abnormal state which is depicted in 

 text-fig. 4. In tlie latter one sees the mucous membrane (A) 

 reflected on to the posterior cartilaginous plate (B). Then comes 

 the oesophageal opening. Before it are the anterior cartila- 

 ginous plate (D), a small groove, and the posterior surface of the 

 larynx (C). 



The folds of mucous membrane (A) merit attention. In the 

 normal condition a vertical ridge runs down the lateral walls of 

 the pharynx and cesophagus, beginning at the posterior faucial 

 pillar at the level of the upper border of the tonsillar pit, and 

 ending at the level of the middle of the larynx. At the level of 

 the most expanded part of the larynx, several horizontal folds 

 run round the entire circumference of the pharynx and oeso- 

 phagus. The vertical ridge, the posterior pillai'S of the fauces, 

 and the side of the larynx enclose a small triangular recess. 



Text-figure 3. Text-figure 4. Text-fieure 5. 



Text-fig. 3. — The esophageal opening. Text-fig. 4. — Sagittal section of 

 abnormal specimen. Text-fig. 5. — Sagittal section of normal specimen. 

 In these D is the anterior cartilaginous plate, and A, B, C are the same 

 as in text-figs. 1 and 2. 



In the abnoi'mal specimen a ridge runs horizontally round the 

 cesophagus, beginning at the angles of the epiglottis, and it 

 bomids a deep recess on each side of the larynx. The mucous 

 membrane is reflected on to the posterior cartilaginous plate 

 (text-fig. 4), thereby forming a small pocket. From the ridge 

 horizontal folds tui-n out and run round the oesophagus. 



The special ^^oints which arise from a consideration of the 

 above abnormality are : — 



1. The origin of the cartilaginous ring. 



2. The manner in which it affects the normal mechanism of 

 deglutition. 



The great rarity of this condition, and the absence of specimens 

 sli owing gradations between the normal and the cartilaginous 

 ring described above, make all opinions as to its nature pui'ely 

 hypothetical. My oAvn opinion is that the development of the 

 cricoid cartilage has gone wrong, and the halves, or one of them, 

 which fuse to close in the postei'ior part of the laryngeal ca.vity, 

 have or has sent processes backwards; these have joined behind 

 to form the catilaginous plate (text-fig. 2, B), or one has grown 

 round and I'ejoined the cartilage again. The anterior plate 

 (text-fig. 2, D) is immovably fixed to the back of the cricoid 



