380 THE BRANCHIAL CLEFTS AND THEIR RELATION TO NERVES. 



palate, constituting cleft palate. Both conditions may occur on one or both sides. From the 

 posterior iart of the first branchial arch are formed the malleus (ossified at the 4th month), and 

 Meckel' 8 cartilage (fig. 673), which proceeds from the latter behind the tympanic ring as a 

 long cartihvnnous process, extending along the inner side of the lower jaw, almost to its middle. 

 Jt disapiK-ars after the 6th month ; still its posterior part forms the internal lateral ligament of 

 the maxillarv articulation. Near where it leaves the malleus is the processus Foln (Baumilllcr). 

 A iart of its median end ossifies, and unites with the lower jaw. The lower jaw is laid down in 

 membrane from the first branchial arch, while the angle and condyle are formed from a 

 cartilaginous process. The union of both bones to form the chin occurs at the 1st year. From 

 the superior maxillary process are formed the inner lamella of the pterygoid process, the palatine 

 process of the upper jaw, and the palatine bone at the end of the 2nd month, and lastly the 

 malar bone. . , , _ . .. , ... -a 



The second arch [hyoid], arising from the temporal bone, and running parallel with the 

 first arch, gives rise to the stapes (although according to Salensky, this is derived from the first 

 arch), the eminentia pyramidalis, with the stapedius muscle, the incus, the styloid process of 

 the temporal bone, the (formerly cartilaginous) stylohyoid ligament, the smaller cornu of the 

 hyoid bone, and lastly the glosso-palatine arch (Sis). .--.- 



"The third arch (thyro-hyoid) forms the greater cornu and body of the hyoid bone and the 

 pharyngo-palatine arch (His). 

 The fourth arch gives rise to the thyroid cartilage (His). 



Branchial Clefts. The first branchial or visceral is represented by the external auditory 

 meatus, the tympanic cavity, and the Eustachian tube ; all the other clefts close. Should one 

 or other of the clefts remain open, a condition that is sometimes hereditary in some families, a 

 cervical fistula results, and it may be formed either from without or within. Sometimes only 

 a blind diverticulum remains. Branchiogenic tumours and cysts depend upon the branchial 

 arches (R. Vulkmann). 



[Relation of Branchial Clefts to Nerves. It is important to note that the clefts in front of 

 the mouth (pre-oral), and those behind it (post-oral), have a relation to certain nerves. The 

 lachrymal slit between the frontal and nasal processes is supplied by the first division of 

 th, trigeminus. The nasal slit between the superior maxillary process and the nasal process is 

 supplied by the bifurcation of the third nerve. The oval cleft, between the superior maxillary 

 processes and the mandibular arch, is supplied by the second and third divisions of tJie trige- 

 minus. The first post-oral or tympanic-Eustachian cleft, between the mandibular arch (1st) 

 and the hyoid arch, is supplied by the portio dura. The next cleft is supplied by the glosso- 

 pharyngeal, and the succeeding clefts by branches of the vagus.] 



The thymus and thyroid glands are formed as paired diverticula from the epithelium cover- 

 ing the branchial arches. The epithelium of the last two clefts does not disappear (pig), but 

 proliferates and pushes inwards cylindrical processes, which develop into two epithelial vesicles, 

 the ]>aired commencement of the thyroid glands. These vesicles have at first a central slit, 

 which communicates with the pharynx ( Wblfier). According to His, the thyroid gland appears 

 as an epithelial vesicle in the region of the 2nd pair of visceral arches in front of the tongue 

 in man at the 4th week. Solid buds, which ultimately become hollow, are given off from the 

 cavity in the centre of the embryonic thyroid gland. The two glands ultimately unite together. 

 The only epithelial part of the thymus which remains is the so-called concentric corpuscles 

 'p. 154). According to Born, this gland is a diverticulum from the 3rd cleft, while His ascribes 

 its origin to the 4th and 5th aortic arches in man at the 4th week. The carotid gland is of 

 epithelial origin, being a variety of the thyroid (Stieda). 



The Extremities. The origin and course of the nerves of the brachial plexus (p. 616) show 

 that the upper extremity was originally placed much nearer to the cranium, while the position 

 of the posterior pair corresponds to the last lumbar and the 3rd or 4th sacral vertebrae (His). 



The clavicle, according to Bruch, is not a membrane bone, but is formed in cartilage like 

 the furculum of birds (Gcgcnbaur). At the 2nd month it is four times as large as the upper 

 limb ; it is the first bone to ossify at the 7th week. At puberty a sternal epiphysis is formed. 

 Epistemal bones must be referred to the clavicles (Gbttc). Ruge regards pieces of cartilages 

 existing between the clavicle and the sternum as the analogues of the episternum of animals. 

 The clavicle is absent in many mammals (carnivora) ; it is very large in nying animals, and in 

 the rabbit is half membranous. The furculum of birds represents the united clavicles. 



The scapula at first is united with the clavicle (Rathke, Gbtte), and at the end of the 2nd 

 month it has a median centre of ossification, which rapidly extends. Morphologically, the 

 accessory centre in the coracoid process is interesting ; the latter also forms the upper part of 

 the articular surface. In birds the corresponding structure forms the coracoid bone, and is 

 united with the sternum ; while in man only a membranous band stretches from the tip of the 

 coracoid process to the sternum. The long, basal, osseous strip corresponds to the supra- 

 scapular bone of many animals. The other centres of ossification are one in the lower angle, 

 two or three in the acromion, one in the articular surface, and an inconstant one in the spine. 

 Complete consolidation occurs at puberty. 

 The humerus ossifies at the 8th to the 9th week in its shaft. The other centres are one in 



