572 



MR. J. B. SUTTON ON THE CRANIAL ARCADE. [DeC. 2, 



The Palato-pterijgoid Arcade. 



Whilst working over a considerable number of skulls of early- 

 human fcEtuses, I was led to look into the early conditions of the 

 auditory ossicles and the associated branchial bars ; in the course 

 of the investigation the following facts came to light. 



Early in foetal life, at about the time the skull begins to chondrify, 

 there may be seen running from the malleus, and continuous with 

 it, a rod of cartilage which extends downwards to near the extremity 

 of the fronto-nasal cartilage. Its relation to the Meckelian cartilage 

 and the tiiyroid arch is shown diagrammatically in fig. 2, where a 

 point of considerable importance is illustrated, viz. that the nerve 

 known in human anatomy as the great superficial petrosal or vidian, 

 bears the same morphological relation to the 7th cranial nerve and 

 the superior maxillary branch of the 5th as does the chorda tympani 

 to the 7th and the inferior maxillary division of the 5th (see diagram). 



To return to the bar of cartilage. Later on in development this 

 bar undergoes metamorphosis, as follows : — 



(a) The inferior end of the cartilage is ossified and is recognized 



Fi-. 3. 



E.C 



('. The Chondro-crauium of a liuman foetus at the tliird niontli, with the asso- 

 ciated cartilaginous bars. 



F.N.P. Pronto-uasal plate. T.T. Tegmen tympani. E.O. Eustachian 

 cartilage. M.C. Meckel's cartilage. S.C. Styloid cartilage. 

 b. The later modification of the arches. 

 1st arch. — I.P. Internal pterygoid palate. E.C. Cartilaginous portion of the 

 Eustachian tubes. Lig. Ant. lig. of the malleus. 2nd arch. — Inf. 

 maxilla, -with long internal lateral ligament of the lower jaw. 3rd areh. — • 

 Hyoid bone. S.H. Lig. Stylo-hyoid hgament. S.P. Styloid process. 

 T.H. Tympano-byal and incus. 



