VARIATIONS IN THE SKELETON. 279 



in front of it. (Orbito-maxillary-frontal suture. A, Thomson, Journ. Anat. and Physiol. 

 vol. xxiv. p. 349.) Division of the lamina papyracea by a vertical suture into an anterior and 

 posterior part has been frequently recorded. The number of the conchse may be increased from 

 two to four, or may be reduced to one. (Report of Committee of Collect. Invest., Journ. Anat 

 and Physiol. vol. xxviii. p. 74.) 



Maxillae. Not infrequently there is a suture running vertically through the bar of bone 

 which separates the infra-orbital foramen from the infra-orbital margin. Through imperfections 

 in ossification, the infra-orbital canal may form an open groove along the floor of the orbit. 



Duckworth records four instances of a spinous process projecting inwards into the apertura 

 piriformis from the lower part of the nasal notch. A case has been described (Fischel) in which 

 there was complete absence of the premaxillae, together with the incisor teeth. 



A not uncommon anomaly is the occurrence of a rounded elongated ridge extending along 

 the interpalatal or intermaxillary sutures on the under surface of the hard palate. This is called 

 the torus palatinus, and is of interest because its presence has given rise to the assumption that it 

 was due to a pathological growth. (See Stieda, Virchow's Festschrift, vol. i. p. 147.) 

 The sulcus lacrimalis may be constricted towards its centre. 



A part of the maxillary sinus may be constricted off anteriorly and, owing to its relation to 

 the naso-lacrimal duct, is called the recessus lacrimalis. 



Underwood (Journ. Anat. and Physiol. vol. xliv. p. 359) records the occurrence of all but 

 complete septa dividing the cavity of the maxillary sinus. 



Zygomatic Bone. Cases of division of the zygoma tic bone by a horizontal suture have been 

 recorded, as well as instances of its separation into two parts by a vertical suture. Owing to the 

 supposed more frequent occurrence of this divided condition in Asiatics the zygomatic has been 

 named the os Japonicum. Barclay Smith (" Proc. Anat. Soc.," Journ. Anat. and Physiol., April 1898, 

 p. 40) describes a case in which the zygomatic bone was divided into two parts, an upper and 

 lower, by a backward extension of the maxilla, which articulated with the zygomatic process of 

 the temporal, thus forming a temporo-maxillary arch. Varieties of a like kind have also been 

 described by Gruber and others. Cases have been noted where, owing to deficiency in the develop- 

 ment of the zygomatic, the continuity of the zygomatic arch has been incomplete. 



Nasal Bones. The size and configuration of the nasal bones vary greatly in different races, 

 being, as a rule, large and prominent in the white races, and flat and reduced in size, as well as 

 depressed, in the Mongolian and Negro stock. Complete absence of the nasal bones has been 

 recorded, and their division into two or more parts has also been noted. Obliteration of the 

 internasal suture is unusual ; it is stated to occur more frequently in negroes, and is the 

 recognised condition in adult apes. 



Duckworth has recorded a case (Journ. Anat. and Physiol. vol. xxxvi. p. 257) of undue extension 

 downwards of the nasal bone, which may be perhaps accounted for on the supposition that the 

 lower part is a persistent portion of the premaxilla. 



Lacrimal. The lacrimal is occasionally absent. In some cases it is divided into two 

 parts ; in others replaced by a number of smaller ossicles. In rare instances the hamulus may 

 extend forwards to reach the orbital margin, and so bear a share in the formation of the face, as in 

 lemurs (Gegenbauer). In other instances the hamulus is much reduced in size. Occasionally 

 the lacrimal is separated from the lamina papyracea of the ethmoid by a down-growth from 

 the frontal, which articulates with the frontal process of the maxilla, as is the normal disposition 

 in the gorilla and chimpanzee. (Turner, Challenger Reports, " Zoology," vol. x. Part IV. Plate I. ; 

 and A. Thomson, Journ. Anat. and Physiol, London, vol. xxiv. p. 349.) 



Inferior Concha. A case in which the inferior conchte were absent has been recorded 

 by Hyrtl. 



Vomer. Owing to imperfect ossification there may be a deficiency in the bone, filled up 

 during life by cartilage. The separation of the two lamellae along the anterior border varies 

 considerably, and instances are recorded where they were separated by a considerable cavity 

 within the substance of the bone. Instances of an extension forwards of the sphenoidal air 

 sinus into and separating the laminae of the bone have also been described. The spheno-vomerine 

 canal is a minute opening behind the rostrum of the sphenoid, and between it and the alaa of the 

 vomer, by which the nutrient artery enters the bone. 



Palate Bones. The occurrence of a torus palatinus may be noted (see Variations of Maxilla). 

 Mandible. Considerable differences are met with in the height of the coronoid process : 

 usually its summit reaches the same level as the condyle, or slightly above it ; occasionally, how- 

 ever, it rises to a much higher level; in other cases it is much reduced. These differences 

 naturally react on the form of the mandibular notch. The projection of the mental protuberance 

 is also liable to vary. Occasionally the mental foramen is double, and sometimes the mylo-hyoid 

 groove is for a short distance converted into a canal There is often a marked eversion of the 

 angle of the mandible, which Dieulafe homologises with the angular apophysis met with in 

 lemurs and carnivora. 



Clavicle. The clavicles of women are more slender, less curved, and shorter than those of 

 men. In the latter the bone is so inclined that its acromial end lies slightly, higher or on the same 

 level with the sternal end. In women the bone usually slopes a little downward and laterally. 

 The more pronounced curves of some bones are probably associated with a more powerful 

 development of the pectoral and deltoid muscles, a circumstance which also affords an explana- 

 tion of the differences usually seen between the right and left bones, the habitual use of the right 



18 b 



