64 SPECIAL ANATOMY. 



a. External surface, presents : Spina mentalis externa. To the outer side of 

 this foramen mentale, which is the exit from the Canal, alveolaris, for Nerv. Art. 

 el Ven. alveol. inferior. 



b. Internal surface, presents : in the centre, Spina mentalis internet, on 

 either side processus geni, four tubercles, sometimes surfaces, the two superior 

 for the genio glossi, the two inferior for the Gen io-Hyoidei muscles, and a 

 ridge the Mylo-hyoid for the mylo-hyoideus muscle ; above this a superficial 

 fossa corresponding to the Sublingual, and one below to the Submaxillary 

 gland. In the centre also a nutritious foramen. 



c. Superior border, limbus alveolaris inferior, behind, thicker than before, 

 presents : sixteen sockets, alveoli, for sixteen teeth with elevations, Juga alve- 

 olaria, for the levator menti and incisivi muscles. 



d. Inferior border, base, thick with an anterior lip for the muse, triangular., 

 quadratus menti et platysmamyoides, and two posterior surfaces for the ante- 

 rior bellies of the m. digastricus. 



2. Kami, ascend at a right angle, in the adult, angulus maxill. infer., from 

 the body, and terminate in the temporal fossa by two processes. 



a. Surfaces. 1. External, flat, rough, for muse, masseter, anterior to which, 

 sometimes, a very slight groove, for art. facia/is. 2. Internal, also rough, for 

 m. Pterygoid. intern., with foram. maxillar. poster., for inferior maxillary or 

 dental nerve. To the borders of the foramen is attached the lig. lateral, intern., 

 and close to it is the Sulcus myloh.yoi.deus, for the nerv. mylohyoid. 



b. Borders: posterior, for Parotid, and below for attachment of Stylo max- 

 illary ligament. Anterior, grooved ; the ridge or continuation of the lined 

 obliq. extern, et intern. 



c. Processes: 



1. Anterior, Proc. coronoideus, triangular, the apex free, for muse. Tem- 

 poralis. 



2. Posterior, Proc. condyloideus, articular process, unites in the Glenoid 

 cavity with the os Temporum. It presents the neck, Col/um Condyli and the 

 fossa for the muse. Pterygoid. extern. Between the two processes: Incisura 

 semilunaris seu sigmoidea, for nerves and vessels. 



Structure. Compact, bony tissue, on the surfaces, in the inte- 

 rior Diploe. The canal for the nerves and vessels of the teeth 

 follows the linea obliq. internet, communicates in this course by 

 one foramen, two, with the alveoli, divides in the region of the 

 Bicuspides teeth into two short canals, one of which opens at the 

 foram. mentale, the other passes as far forwards as the first 

 incisor tooth. Lying at the inferior border, before the appear- 

 ance of the teeth, they are associated together, and the canal, alv. 

 inf. always moves upwards as age advances, or, rather bone is 

 developed beneath it, and thus it appears to ascend. 



Development. Next to the clavicle the earliest perfectly formed 

 bone ; in mammals, it presents even in the 2d month one osseous 

 centre upon either side for the body. Soon after birth the two 

 halves unite together. In the new-born infant the lower jaw is 

 very small, the angle still obtuse, the alveolar processes broad. 

 In old age the alveolar processes disappearing after the teeth have 

 fallen out, the lower jaw becomes smooth, thick, and again small. 



