The foramina of the carotid circulation consist of pattern 1 (sensu Voss, 1988); a thick alisphenoid
strut is present, and the subsquamosal fenestra is large (Figs.
First ossification of Dentary Premaxilla Maxilla Frontal Jugal Parietal Squamosal Alisphenoid
Basioccipital Basisphenoid Exoccipital Periotic Other skeletal elements Membrane bones approach midline Cartilage in basioccipital region Closure of secondary palate First appearance of tooth buds Differentiation of malleus and incus Differentiation of condylar cartilage Joint capsule at dentary-squamosal joint Muscle First alignment of myoblasts (tongue) First appearance of striations Craniofacial muscles distinguishable Central nervous system Evagination of telencephalon Differentiation of pigment in retina Connections between olfactory nerve and epithelium Layering in cortex Swelling of thalamus and hypothalamus Primary lens cells fill lens vesicle
Character Irenomys Euneomys Neotomys Tail length >HBL <HBL <HBL Palate topography flat, ridged, ridged, uncomplicated foraminated foraminated Premaxillo-maxillary dorso-ventrally sharply sharply suture oriented angled angled Spinous process on absent absent present zygomatic plate Interfrontal present absent present fontanelles Alisphenoid
strut present present (a) absent Facial circulation complete complete incomplete Caecum complex single single Cornified stomach extensive extensive reduced epithelium 2n (FN) 64 (98) (b) 34-36-42 70 (68) (d) (62 to 66) (c) (a) Contrary to the condition noted by Steppan (1995:40), we recorded the alisphenoid
strut in Euneomys as present and bony.
77 (Table 1), the presence of an anteromedial alisphenoid
process on the auditory bullae, interorbital region with beaded supraorbital margins, and the absence of a maxillary fenestra (Fig.