THE SUTURES. 207 



$l>Jn-ii',i<lnl sutures. These sutures can also be seen in the orbit, and form part of 

 the so-called t/-'i/<s>-' /< //-/,// suture. The posterior portion is formed between the 

 parietal bone above and the great wing of the sphenoid, the squamous and mastoid 

 portions of the temporal bone, forming the spheno-parietaL squamo-parietal. and 



>'.'ta? sutures. 



The Spheno-parietal is very short : it is formed by the tip of the great wing of 

 the sphenoid, which overlaps the anterior inferior angle of the parietal bone. 



The Squamo-parietal, or Squamous Suture, is arched. It is formed by the 

 squamous portion of the temporal bone overlapping the middle division of the 

 lower border of the parietal. 



The Masto-parietal is a short suture, deeply dentated. formed by the posterior 

 inferior angle of the parietal and the superior border of the mastoid portion of the 

 temporal. 



The sutures at the base of the skull are the basilar in the centre, and on each 

 side the petro-occipital^ the imisto-oecipitaL the petro-sphenoidal, and the squamo- 

 : il. 



The Basilar Suture is formed by the junction of the basilar surface of the 

 occipital bone with the posterior surface of the body of the sphenoid. At an early 

 period of life a thin plate of cartilage exists between these bones, but in the adult 

 they become fused into one. Between the outer extremity of the basilar suture 

 and the termination of the lambdoid an irregular suture exists, which is subdivided 

 into two portions. The inner portion, formed by the union of the petrous part of 

 the temporal with the occipital bone, is termed the petro-occipital. The outer 

 portion, formed by the junction of the mastoid part of the temporal with the 

 occipital, is called the masto-occipital. Between the bones forming the petro- 

 occipital suture a thin plate of cartilage exists; in the masto-occipital is occa- 

 sionally found the opening of the mastoid foramen. Between the outer extremity 

 of the basilar suture and the spheno-parietal an irregular suture may be seen, 

 formed by the union of the sphenoid with the temporal bone. The inner and 

 smaller portion of this suture is termed the petro-sphenoidal ; it is formed between 

 the petrous portion of the temporal and the great wing of the sphenoid : the outer 

 portion, of greater length and arched, is formed between the squamous portion 

 of the temporal and the great wing of the sphenoid ; it is called the squamo- 

 sphenoidal. 



The cranial bones are connected with those of the face, and the facial bones 

 with each other, by numerous sutures, which, though distinctly marked, have 

 received no special names. The only remaining suture deserving especial con- 

 sideration is the transverse. This extends across the upper part of the face, and 

 is formed by the junction of the frontal with the facial bones : it extends from the 

 external angular process <>f one side to the same point on the opposite side, and 

 connects the frontal with the malar, the sphenoid, the ethmoid, the lachrymal, the 

 superior maxillary, and the nasal bones on each side. 



The sutures remain separate for a considerable period after the complete for- 

 mation of the skull. It is probable that they serve the purpose of permitting the 

 growth of the bones at their margins, while their peculiar formation, together 

 with the interposition of the sutural ligament between the bones forming them, 

 prevents the dispersion of blows or jars received upon the skull. Humphry 

 remarks, " that, as a general rule, the sutures are first obliterated at the parts in 

 which the ossification of the skull was last completed viz. in the neighborhood 

 of the fontanelles : and the cranial bones seem in this respect to observe a similar 

 law to that which regulates the union of the epiphyses to the shafts of the long 

 bon The same author remarks that the time of their disappearance is 



extremely variable : they are sometimes found well marked in skulls edentulous 



with age. while in others which have onlv just reached maturitv thev can hardly 



. j j 



be traced. 



