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 |   Related post: lateral cervical and thoracic walls. The third and fourth arches do not unite, however, with the hyoid arch. The third arch unites with the lateral cervical wall over the fourth arch, and in its further development gives rise to the second cavity and an infundibular passage, the fundus and infundibulum praecervicale. The mandibular arch maintains its shape to a large extent in its further development, and, together with the first cleft, contributes to tlie formation of the external ear. The external clefts of the Cystone Himalaya three following arches are gradually erased after the closure of the cervical sinus and are of secondary importance, lying as they do behind the very large hyoid arch, which is represented by all that superficial portion of the neck which we know as the anterior cervical triangle. By the intrusion of the ecto- dei'm and the advance of the oral extremity of the mesenteron Read before the New York Surgical Society, April 15, 1891. (the digestive tract), the entoderm and ectoderm meet and are erased, forming at their j)f)int of erasure the isthmus faucium. By the growtli and union of the palate and the frontal process, the stomodanun is thus divided into three parts — the nares and the mouth — while upon the lateral walls of the mesenteron are seen four protrusions — the internal as- pect of the arches, with their Buy Cystone clefts. The first internal cleft gives origin to the internal ear — i. e., the Eustachian tube and the middle ear — separated from the external ear (the first external cleft) by the mem- brana tympani. The second internal cleft is found in that portion of the pharynx known as the fossa of Kosenmiiller and in the su- pratonsillar fossa. It extends as a long circular canal toward the second externa! cleft, where it is closely connected with the sinus cervicalis on its anterior wall (Rabl's Kiemengang). The third internal cleft is represented by that portion in front of the plica nervi laryngei. It extends toward and is closely applied to the third external cleft (the floor of the fundus prtecervicalis), where, dividing into a dorsal and a ventral limb, it gives origin by these to the carotid (Steda) and thymus glands (Born). The fourth internal cleft and its appendix, the fundus branchialis, is to be found in the sinus pyriformis. It never reaches its corresponding external cleft, but remains sepa- rated from it by a well-marked amount of mesoderm. It is thus excluded from any connection with the cervical sinus. In the median line of the neck the arches approaching one another leave a triangular space, the meso-branchial field (His), bounded laterally and above by the opercular pro- cesses of the second arch ; below, by the thoracic wall. The union of the first arch above is direct, while in the second and third arches it takes place indirectly through the body of the hyoid bone. As a result, the internal margins of the opercular pro- cesses of the sinus cervicalis converge in the median line at the hyoid bone in an oblique Cystone Tablets angle, and are gradually united with the primary thoracic wall, which advances as a tri- angular piece between them. In the upper portion of this mesobranchial field is seen the tuberculum impar, the future tongue, and below it the furcula, which is later to become the epiglottis and ary- tseno-epiglottic folds. The tuberculum impar is separated from the mandibular arch by a groove, the submaxillary groove, and from the ends of the two arches behind by a deep groove, the lingual duct. As growth continues, the ventral ends of the second and third arches on each side coalesce, and, extending behind the tuberculum impar, join those of the opposite side be- tween the tuberculum in front and the divided median emi- nence behind, from which the larynx is to develop. The groove between the united bases of the second and third arches and the body of the tongue is the V-line Himalaya Cystone along which the circumvallate papilla; develop. The frenum of the tongue is the primitive union with the mandibular arch. The prominent anterior edge of the second arch is the anterior llMiTLKY: (  )NUh:MTAL TUMiUiS OF THE NECK. [N. Y. Med. Joni., pillar of the fHiiccH, while tlic liitcral jfloKso-cpijjlottic fold is till' poNtcrinr cdirt" of tlic tliirtti(iis is a fold pjissiiii; from tin* iiiiitrd cdj^cs of the third iiiclit's to the cpiLflott is. The Irijfi-iniiial mci nf thf toiij^iic is rcpn'sriilcil liy llic liilM-iciihiin iiiipiir, and is in- iicivntcd liy tin- t liiji'iiiiiial iicrvi-, the axial iktvc of the lirst arch, 'I'hf y;losso-pliaiv nigral area is that portion of the toinfiu' hcliiiid the (•ii
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