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On some of the Subaxial Arches in Man. 



[Mar. 16, 



II. " On the formation of some of the Subaxial Arches in Man/ 

 By George W. Callender, Assistant Surgeon to, and Lec- 

 turer on Anatomy at St. Bartholomew's Hospital. Communi- 

 cated by J. Paget, F.R.S. Received February 17, 1871. 



(Abstract.) 



In the term subaxial arches is included all those which grow out in front 

 of the notochord. The first forms the nasal passages, the second forms 

 chiefly the superior maxilla, the third is the mandibular, the fourth the 

 lingual, the fifth the hyoid, the sixth the laryngeal, whilst the seventh, 

 which is distinguished as the exoccipital arch, forms the shoulder- girdle 

 and the thoracic extremity of either side. 



The consideration of the connexion of the first four with the cranial 

 cartilages is for the present deferred ; and this communication relates to 

 those arches which grow into the cervical region, and to that period of 

 their growth which lies between the fifth and twelfth weeks of foetal life. 



The fourth subaxial arch, the lingual, grows out below the mandibular, 

 and bears upon its anterior extremity the tissue which developes into the 

 tongue. Its connexion with this anterior portion ceases to be recognized 

 at an early period, and about the eleventh week it consists of five portions, 

 (1) cartilage from the base of the skull, (2) a short piece of membrane, 

 (3) a second very small rod of cartilage, these forming about one-half of 

 its length, (4) a long strip of membrane, and (5) a nodule of cartilage 

 within the lesser or anterior horn of the hyoid bone. 



The fifth subaxial arch, the hyoid, grows in common with the sixth as a 

 layer of membrane from the basioccipital region. The posterior portion 

 of it forms the middle constrictor muscle ; the remainder is cartilaginous, 

 and grows into the greater or posterior horn and the body of the hyoid 

 bone. 



The sixth subaxial arch, the laryngeal, begins in membrane which forms 

 the inferior constrictor. Rising up and thickening in the front of the 

 neck, it encloses the pharynx ; and its inner layer developes a septum, which 

 separates this tube from the larynx. In front, and between this inner 

 layer and that in which the constrictor is formed, a mass of thick granular 

 tissue becomes cartilage, and here the chief cartilages of the larynx are 

 formed. The details of their formation are referred to. 



The thyroid body is developed in this arch, and it serves as a girdle to 

 surround and keep in place the continuation of the air-tube towards the 

 thorax. Its relation to the branchial arches is also referred to. 



After mentioning the reason for calling the seventh arch the exoccipital, 

 its growth from the basioccipital and exoccipital cartilage regions is de- 

 scribed, with its ending in two processes which grow out as the clavicle 

 and the scapula. The relations of the clavicle to the sternum and first rib 

 are related, as also its change in direction from a nearly vertical to a hori- 



