SUTURES. OSSA TRIQUETRA. 53 



The schindylesis suture (r%nMji*Hf t a fissure) is the reception of 

 one bone into a sheath or fissure of another, as occurs in the articula- 

 tion of the rostrum of the sphenoid with the vomer, or of the latter 

 with the perpendicular lamella of the ethmoid, and with the crista 

 nasalis of the superior maxillary and palate bones. 



The serrated suture is formed by the interlocking of the radiating 

 fibres along the edges of the flat bones of the cranium during growth. 

 When this process is retarded in the infant by over distention of the 

 head, as in hydrocephalus, and sometimes without any such apparent 

 cause, distinct ossific centres are developed in the interval between the 

 edges ; and, being surrounded by the suture, form independent pieces, 

 which are called ossa triquetra, or ossa Wormiana. In the lambdoid 

 suture there is generally one or more of these bones ; and, in a beauti- 

 ful adult hydrocephalic skeleton in the possession of Mr. Liston, there 

 are upwards of one hundred. 



The coronal suture (fig. 28) extends transversely across the vertex 

 of the skull, from the upper part of the greater wing of the sphenoid 

 to the same point on the opposite side ; it connects the frontal with 

 the parietal bones. In the formation of this suture the edges of the 

 articulating bones are bevelled, so that the parietal rest upon the 

 frontal at each side, and in the middle the frontal rests upon the 

 parietal bones ; they thus afford each other mutual support in the 

 consolidation of the skull. 



The sagittal suture (fig. 28) extends longitudinally backwards 

 along the vertex of the skull, from the middle of the coronal to the 

 apex of the lambdoid suture. It is very much serrated, and serves to 

 unite the two parietal bones. In the young subject, and sometimes 

 in the adult, this suture is continued through the middle of the frontal 

 bone to the root of the nose, under the name of the frontal suture. 

 Ossa triquetra are sometimes found in the sagittal suture. 



The lambdoid suture is named from some resemblance to the Greek 

 letter A, consisting of two branches, which diverge at an acute angle 

 from the extremity of the sagittal suture. This suture connects the 

 occipital with the parietal bones. At the posterior and inferior angle 

 of the parietal bones, the lambdoid suture is continued onwards in a 

 curved direction into the base of the skull, and serves to unite the 

 occipital bone with the mastoid portion of the temporal, under the 

 name of the additamentum sutures lambdoidalis. It is in the lambdoid 

 suture that ossa triquetra occur most frequently. 



The squamous suture (fig. 28) unites the squamous portion of the 

 temporal bone with the greater ala of the sphenoid and with the 

 parietal, overlapping the lower border of the latter. The portion of 

 the suture which is continued backwards from the squamous portion 

 of the bone to the lambdoid suture, and connects the mastoid portion 

 with the posterior inferior angle of the parietal, is the additamentum 

 sutures squamos(R. 



The additamentum suturae lambdoidalis and additamentum suturse 

 squamosae, constitute together the mastoid suture. 



