VARIATIONS IN THE SKELETON. 



be fused anteriorly with the cartilage of the first rib, or the cervical rib may be free. It may 

 in some instances be represented mainly by a ligamentous band, or its vertebral and sternal 

 ends may be alone developed, the intermediate part being fibrous. At times the vertebral end 

 only may be formed, and may be fused with the first rib, thus leading to the formation of a 

 bicipital rib such as occurs in many cetaceans. (For a detailed account of this anomaly see Wingate 

 Tod's paper in the Journ. o/ Anat. and Physiol vol. xlvi. pp. 244-288.) Increase in the number of ribs 

 may also be due to the ossification of the costal element which is normally present in the embryo 

 in connexion with the first lumbar vertebra. (Rosenberg, Morph. Jahrb. i.) Reduction in the 

 number of ribs is less common. The twelfth rib rarely aborts ; in some cases the first rib is 

 rudimentary. Cases of congenital absence of some of the ribs have been recorded by Hutchinson, 

 Murray, and Ludeke. Fusion of adjacent ribs may occur. (Lane, Guy's Hosp. Reports, 1883.) 

 In this way, too, the occurrence of a bicipital rib is explained. This anomaly occurs most 

 usually in connexion with the first rib, which either fuses with a cervical rib above or with the 

 second rib below. 



Variations in form may be in great part due to the occupation of. the individual and the con- 

 stricting influence of corsets. Independently of these influences, the ventral part of the body is 

 sometimes cleft so as to appear double ; at other times the cleft may be incomplete so as to form 

 a perforation. Occasionally adjacent ribs are united towards their posterior part by processes 

 having an intermediate ossicle between (Meckel), thus recalling the condition normally met with 

 in birds ; more usually, however, the bony projections are not in contact. 



The number of true or vertebro-sternal ribs may be reduced to six, or increased to eight (vide 

 ante, p. 276). Dwight (Journ. of Anat. and Physiol. vol. xlv. p. 438) describes a series of cases in 

 which the interval between the transverse process of the first thoracic vertebra and the neck of 

 the first rib is bridged across or converted into a linear cleft by a dorsal extension from the neck 

 of the rib. 



Costal Cartilages. Occasionally a costal cartilage is unduly broad, and may be pierced by a 

 foramen. The number of costal cartilages connected with the sternum may be reduced to six or 

 increased to eight (see p. 276). In advanced life there is a tendency towards ossification in the 

 layers underlying the perichondrium, more particularly in the case of the first rib cartilage, in 

 which it may be regarded as a more or less normal occurrence. 



Frontal Bone. The variation most frequently met with is a persistence of the suture 

 which unites the two halves of the bone in the infantile condition : skulls displaying this peculiarity 

 are termed metopic. The researches of various observers Broca, Ranke, Gruber, Manouvrier, 

 Anoutchine, and Papillault (Rev. mens. de I'ecole d'Anthropol. de Paris, anne"e 6, n. 3) point to the 

 more frequent occurrence of this metopic suture in the higher than in the lower races of man ; and 

 Calmette asserts its greater frequence in the brachy cephalic than the dolichocephalic type. 

 Separate ossicles (ossa suturarum) may occur in the region of the anterior fontanelle. The fusion 

 of these with one or other half of the frontal explains how the metopic suture is not always in 

 line with the sagittal suture (Stieda, Anat. Anz. 1897, p. 227) ; they occasionally persist, however, 

 and form by their coalescence a bregmatic bone. (G. Zoja, Bull. Scientific, xvii. p. 76, Pa via.) 

 Turner (Challenger Reports, part xxix.) records an instance of direct articulation of the frontal 

 with the frontal process of the maxilla in a Bush skull, and other examples of the same anomaly, 

 which obtains normally in the skulls of the chimpanzee and gorilla, have been observed. (Journ. 

 Anat. and Physiol. vol. xxiv. p. 349.) 



There is sometimes a small arterial groove just medial to the supra-orbital notch or foramen, 

 and occasionally the latter is double, the lateral aperture piercing the orbital margin wide of 

 its middle point. Frequently the bone corresponding to the floor of the lacrimal fossa displays a 

 cribriform appearance. 



Schwalbe (1901) records the presence of small independent ossicles (supra-nasal bones) in the 

 anterior part of the metopic suture. The same anatomist has also directed attention (Zeit. f. 

 Morph. und Anthr. vol. iii. p. 93) to the existence of the metopic fontanelle, first described by 

 Gerdy, and the occurrence of metopic ossicles (ossa interfrontalia) and canals. 



Parietal. A number of cases have been recorded in which the parietal is divided into an 

 upper and lower part by an antero-posterior suture parallel to the sagittal suture. Corami 

 (Atti d. XL Congr. Med. Internaz. Roma, 1894, vol. v.) records a case in which the parietal was in- 

 completely divided into an anterior and posterior part by a vertical suture. A tripartite 

 condition of the bone has also been observed (Frasetto). The parietal foramina vary greatly 

 in size, and to some extent in position. They are sometimes absent on one or other side, 

 or both. They correspond in position to the sagittal fontanelle. Sometimes the ossification 

 of this fontanelle is incomplete and a small transverse fissure remains. The parietal foramen 

 represents the patent lateral extremity of this fissure after its edges have coalesced. 

 Occasionally in the region of the anterior fontanelle an ossicle of variable size may be met witli. 

 This is the so-called pre-interparietal bone. According to its fusion with adjacent bones 

 may disturb the direction of the sagittal suture. 



Occipital. The torus occipitalis transversus is the term applied to an occasional eleva- 

 tion of the bone which includes the external occipital protuberance and extends laterally along 

 the superior curved line. Occasionally an emissary vein pierces the bone opposite the occipital 

 protuberance. In about 15 per cent, of cases the hypoglossal canal is double. Mu< 

 three or even four foramina may be met with. The most striking of the many variations to 

 which this bone is subject is the separation of the upper part of the squamous part 

 occipital to form an independent bone the interparietal bone, called also, from the 



