1272 A MANUAL OF ANATOMY 



Myotomes ot Visceral Arches. — ^The cervical myotome in each arch gives rise 

 to certain muscles. The myotome of the Jirst arch furnishes (i) the anterior 

 belly of the digastric; (2) the mylo-hyoid; and (3) the muscles of mastication — 

 namely, (a) masseter, (b) temporal, (c) external pterygoid, and (d) internal 

 pterygoid. 



The myotome of the second arch furnishes (i) the posterior belly of the 

 digastric; (2) the stylo-hyoid; and (3) the stapedius. From this myotome are 

 also derived the muscles ol expression on the face and epicranial region, as 

 well as the platysma. 



The myotome of the third arch furnishes the stylo-pharyngeus, and the 

 middle constrictor ol the pharynx may be regarded as derived from it. 



The myotome of the fourth arch (and perhaps that of the fifth arch) may be 

 regarded as furnishing the inferior constrictor of the pharynx. 



Nerves of Visceral Arches — First, or Mandibular (oral). Arch. — The common 

 nerve of this arch is the fifth cranial, or trigeminal, nerve. The inferior 

 maxillary or mandibular division belongs to the mandibular process of the 

 arch, and to its muscles, and the lower teeth of one side ; the superior max- 

 illary division belongs to the maxillary process of the arch, and to the upper 

 teeth of one side; and the ophthalmic division belongs to the supplementary 

 fronto-nasal process (one-half) . 



Second, or Hyoid, Arch. — The nerve of this arch and of the first pharyngeal 

 pouch is the seventh cranial, or facial, nerve. The eighth cranial, or auditory, 

 nerve may be included. 



Third, or Thyro-Hyoid, Arch. — ^The nerve of this arch and of the second 

 pharyngeal pouch is the ninth cranial, or glosso-pharyngeal, nerve. 



Fourth Arch. — ^The nerve of this arch is the superior laryngeal nerve, which 

 is a branch of the tenth cranial, or pneumogastric (vagus). 



Fifth Arch. — The nerve of this arch is the inferior, or recurrent laryngeal, 

 nerve, which is a branch of the pneumogastric. 



The bar of cartilage, in each arch, is developed in the mesenchyme, which 

 forms the core of the arch. 



Metamorphoses of the Visceral Arches. 



First Visceral, or Mandibular, Arch. — This arch is situated, as stated, between 

 the first pharyngeal pouch and the stomodaeum or primitive oral cavity. Its 

 artery is the first primitive aortic arch; its common nerve is the fifth cranial 

 or trigeminal nerve; and its cartilaginous bar is known as Meckel's cartilage. 

 The ventral end of this cartilage meets its fellow of the opposite side, and 

 is joined to it by connective tissue. The dorsal end is related to the periotic 

 cartilaginous capsule, and furnishes an offshoot, called the maxillary process. 

 For a full account of the transformation of the first visceral arch see the 

 Development of the Skull. It will be sufficient here to note the following 

 points : 



1. The upper or dorsal end of Meckel's cartilage, becoming ossified, gives 

 rise to the malleus, and probably the incus. 



2. The lovoer or ventral end of Meckel's cartilage gives rise to the indsor 

 portion of the mandible. 



3. The part of Meckel's cartilage between the upper and lower ends disap- 

 pears. The membranous investment of the lower or mandibular portion of this 

 part gives rise to the chief part of one-half of the body of the mandible, and 

 the lower half of the ramus as high as the inferior dental foramen. The mem- 

 branous investment of the upper portion, between the periotic cartilaginous 

 capsule and the inferior dental foramen, forms the spheno-mandlbular liga- 

 ment. 



4. The maxillary process, aided by part of the fronto-nasal process — 

 namely, the globular and lateral nasal processes, gives rise to the superior 

 maxilla (see Development of the Skull). 



5 . The upper end of the first arch gives rise to the tragus, and part of the 

 heiix of the pinna. 



Second, or Hyoid, Arch. — This arch is situated, as stated, between the first 

 and second pharyngeal pouches. Its artery is the second primitive aortic 



